That is plan maximum. Most likely nothing would happen, because due to interregnum PLC would be paralysed for months.
This reason is peanuts. The serious reason is that as soon as Charles is going away (which he would as soon as Peter agrees on pre-war borders, which in 1700/01 he would do easily), the Poles suffering from excessively good memory would be dealing with the consequences of their enthusiasm because Peter would be invading the PLC with the obvious consequences: looting, burning, etc. His army was not, yet, up to the Swedish level but PLC is lagging few decades behind: during the GNW both sides had been using it as a battleground with a minimal local opposition.