If the Poles hold the Romanian bridgehead, they will be getting quite a bit of supplies and other goods.
Their air force retreated into Romania on the 17th OTL, it might be delayed a few days ITTL - French and British fighters (MS.406s and Hurricanes), tanks (R35 and Lt Mk VI) and artillery as well as supplies were on their way to Romania OTL. Poland fell fast, so those arms were sold to Romania and Turkey OTL. ITTL, they will reach the Poles and make them much stronger - the Romanians will probably allow the Polish air force to rebuild with MS.406 and Hurricanes. They were very French-friendly OTL until Poland fell and the French did little and they thus re-aligned themselves to German friendship. In late October, the Polish air force, with its experienced and extremely well-trained pilots will be back over Poland (these are the guys that did so well in the Battle of Britain) with MS.406 and Hurricane Is instead of Pzl P.11s. The Luftwaffe will be fighting a two-front war, which will add to the strain.
The French were raising two Polish divisions in France at this time, from Polish guest workers (mostly in the coal mining industry). I guess these troops, with more supplies and weapons, might be shipped to Romania for further transit to the Polish troops in the bridgehead.
Polish stragglers and troops in fortified positions had a surprsing tenacity - I guess small groups of stragglers and refugees wishing to fight will continue to trickle to the bridgehead, and the Germans will need to deal with places such as Modlin, where the Poles OTL only surrendered well after other troops (IIRC).
OTL, the Slovaks were less than enthusiastic to fight against fellow Slavs and the Poles were raising a few exile Czechoslovak battalions - if they maintain a border with Slovakia, I expect Slovak deserters and Czech refugees to enter the Romanian brigdehead in a small but steady trickle - a brigade is possible by November 1939, a division by spring.
The autumn rains were late in 1939, but by mid-October any kind of motorised movement was close to impossible in Poland.
I also guess remnants of the Obrona Narodowa and regular army stragglers will form AK early and harass the Germans mercilessly.
Warsaw turned over to the SS? There's not much of an SS to speak of at this time, and a good part of it has been gutted in the Polish campaign (the Germania regiment was over-run in a Polish counterattack). At this time the SS is the stepchild of the Heer - it gets hand-me-down equipment (MG 35/36, Mauser Schnellfeuer, MG08, Czechoslovak rifles etc) and bad training, which they try to make up for with fanaticism - the Heer regarded them as secon rate units and they suffered massive casualties. It is not until late 1940 that the SS can be described as any kind of elite armed branch (a status they lost 1942, when they started taking forced conscripts and making militia formations).
Thankyou for a very good timeline, consider me painted curious.