I was wondering about what would happen if Von Tresckow's 1943 plot to kill Hitler succeeded, the one where he tried to kill Hitler by putting a bomb on his plane. Did the conspirators have a plan to seize power in Berlin similar to the Valkyrie plan in 1943? If they do and it gets pulled off successfully, what happens from there in terms of the war, potential peace, etc?
They had a plan to seize power in Berlin, yes. Now, it is certainly not sure it would have succeeded, but IMO it is totally unreasonable to assume that if Hitler had died, the rest of the Nazi top echelons would have been surely able to suppress the coup or set up enough armed resistance to unleash a civil war (beyond some hours or days of patchwork skirmishes, that is). That might happen if Himmler escapes death or capture, and retains control of the SS network, but otherwise, we must be mindful of two factors: the Wehrmacht oath of loyalty was to Hitler himself, not to the National-Socialist regime. Also, the Nazi regime was critically reliant on Hitler to maintain cohesion. Him dead, the Heer in early 1943 has very little motivation to give allegiance to any other Nazi top dog, instead of setting up their own junta. And besides the SS network, the Nazi regime has very little ability to successfully stage any armed resistance against a military takeover.
So, the Heer takes over, and stabilizes its power after a few brief skirmishes with the most Nazi diehards among the Gestapo and the SS. They quickly attempt to set up separate peace negotiations with the Western Allies and with Stalin. The former quickly stall because the junta has unrealistic demands, given the political situation in Britain and America (they ask for a free hand in Central-Eastern Europe, in exchange for the liberation of Western Europe). The latter seem more promising, but ultimately stall as well, because of mutual distrust and disagreement about the placement of the border (Stalin asks for the 1941 borders, the junta wants the Dnieper border).
The junta retools and streamlines the German military machine and armament industry, focusing efforts on a few key weapon models and projects, and adopts elastic defense as a strategy. As a result, Summer-Fall 1943 battles on the Eastern Front result in a decisive German victory (they adopt Manstein's Backhand Blow strategy and it is successful, leading to the destruction of the whole southern wing of the Red Army). On the Western Front, the landings in Sicily succeed, but the ones in Salerno and Taranto are a bloody failure. They manage to seize a bridgehead in the tip of Calabria, but a combination of German entrenchment, bad logistics, and worse mountain terrain make any land gains in that area to happen at such a slow pace to make them useless. End of 1943 sees the Germans still entrenched in eastern Ukraine and masters of mainland Europe. The bloody failure of the landings in mainland Italy cause the Western Allies to rethink their strategic options: Roosevelt still pushes for a big amphibious offensive in northern France, but Churchill gets the greenlight for his dearly wished peripheral landings in Norwegia and the Balkans.
1944 sees a long string of massive Russian offensives on the Eastern Front, which the Germans counter by extensive use of elastic defense. The Wehrmacht is gradually forced to cede ground against the onslaught of superior Soviet numbers, but they manage to keep their own resources essentially intact, and make the Soviet bleed massively for every inch of terrain they reconquer and every German soldier they kill. By mid 1944, the Red Army has reached the Dnieper, and by late 1944 the Dvina-Pripet-Bug line, but they are totally exausted, with the USSR scraping the bottom of its manpower reserves. Stalin reluctantly accepts an armistice on the 1939 borders.
On the Western Front, the Allies have stepped up their bombing of Germany but the first German jet fighters are coming into line and making such efforts more and more costly and of questionable effectiveness. The landings in Norwegia and Greece have succeeded, allowing the Western Allies to liberate large tracts of both countries and to put Romanian oilfields and Swedish iron mines in their bombing range, which hampers the German war effort to a significant but not crippling degree. This however causes the German junta to scale down their demands for a peace settlement, to the platform of Germany and its allies keeping their own "ethnic" territories and their national independence and freeing other occupied nations throughout Europe. They go public with their peace offer. Roosevelt remains totally hostile, but Churchill is more pliable. Overlord is either a complete failure (since jet fighters allow the German to make extensive air recognition and seriously contest air superiority and thanks to a timely German counterattack on the beaches) or it manages to make a foothold, but the Allies face terribly high losses for every inch of land they conquer, while German elastic defense is keeping the bulk of the Wehrmacht essentially intact.
A combination of factors (high casualties in Europe, the failure of landings in Italy and possibly in France, the fall of the Nazi regime and the new German goverment's public peace offer, the separate armistice of the Soviets) totally discredit Roosevelt's "unconditional surrender" political platform, and he loses the 1944 elections.
The new Adminstration is more willing to discuss a compromise peace, as it is the British government. In early 1945, a compromise peace is signed alongside the following terms: Germany keeps its 1939 borders, plus Danzig, the Corridor, and Upper Silesia (maybe even Posen, Luxemburg, and Elsass-Lotharingen if D-Day was a failure), Hungary keeps southern Slovakia, Backa, and northern Transylvania, the Baltic countries, Slovenia, and Croatia-Bosnia keep their independence, Italy and Finland keep their 1938 borders (quite possibly Italy keeps Dalmatia as well, since Croatia would be an independent ex-Axis country, too, and the Western Allies would not mind either way too much). The Axis countries liberate all other territories (Norway, Danemark, Netherlands, Belgium, France, 1939 Czechoslovakia, Poland with 1914 Western and 1939 Eastern borders, Greece, Albania, and Serbia), hand over war criminals for a trial in international tribunals, accept Western Allies supervision and inspection rights over their democratization process and gradual disarmement, the Western Allies recognize the separate peace between the Soviets and the Axis on the 1939 borders.