I guess the only question now is will Putin be happy with taking the separatist areas and annexing them to Russia proper, or will he roll the dice and try to take the entirety of Ukraine?

Stopping at the Dnieper River would be logical, but it presents a major problem, especially if the Ukrainian government relocates to Lviv and launches an insurrection to retake the Russian-occupied areas. NATO could quite easily supply a rump Ukrainian state with all manner of weapons, which would pose a real threat of a protracted and bloody insurgency war. Thus, in order to forestall that possibility, there is a likelihood that Putin could decide to continue a military offensive….right up until it runs into the borders of NATO members Poland, Slovakia, Hungary and Romania.