WI Boleslaw the brave keeps some conquests?

OTL after Otto III died in 1002, Boleslaw made deals with claimants in exchange for territory, and occupied Lusatia, Bohemia, Moravia, and Slovakia. Henry II was crowned and managed to defeat Boleslaw by 1005. Slovakia was lost later.

Through different diplomatic or military means could Boleslaw have kept some or all of his conquests?

These areas were still fairly sparsely populated with slavs. If they had been Christianised under the Poles would Czech and Lusatian be today Polish dialects or accents?

Would the capital stay in Poland proper, or move west with the border? Wroclaw?
 
Bolesław actually kept Lusatia, Upper Lusatia and Moravia with the Treaty of Bautzen in 1018. It this debatable, wether he kept Lusatia as fiefdom, or as an integral part of Polish territory. Anyway, all those lands were lost later by Bolesław's son, Mieszko II. AFAIK some Czech historians claimed Moravia was retaken by Bohemia about 1020, but Polish historians put it in 1031.
The problem with early Poland was that king's power was based on his personal army (drużyna). As long as he was able to kept them satisfied with successful conquests and spoils, his position was strong. Bolesław's successes were costly, he managed to antagonize most of Poland's neighbours (except Hungary) and eventually they came back with a vengeance. While Mieszko II was not as incompetent as he was often called in Polish historiography, he was simply unable to resist almost simultanous invasions from Germany, Bohemia and Kiev.
In short: Bolesław took too much lands Poland was actually able to hold and Mieszko II paid the price. However...
About 1027 Mieszko II was supposed to help with his army Ernest II, duke of Swabia in his rebellion against emperor Conrad II. Mieszko did not arrive, and Ernest was imprisoned. A year later Mieszko's army invaded and devastated Saxony. WI Mieszko did arrive in time to actually help Ernest and by some luck they managed to defeat Conrad II? With Ernest as the emperor Mieszko II would have had a very powerful friend, a large success to appease domestic opposition and potentially free hand or even support against Bohemians and Kievans.
 
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