The reason is that, apparently, Dutch has not seen fit to follow English in that spelling change, then. My newspaper is consistently writing Sebastopol. You know how it goes with proper names in different languages.
As far as I can tell from reading up on him, he doesn't seem to have had any chance to be genocidal, being in Nazi prisons for basically all that time? Though from what he did do I'll agree it's rather dubious to put up monuments for him. When you said genocidal my first thoughts were that you were referring to the Holodomor, which made it rather confusing.
As for chopping up - um, yeah, as I said, can't agree with you there, nor do I think it likely. It's possible Putin will manage to get the entire Crimea and not just Sevastopol, but I don't think he's fool enough to try and take more than that, since that alone would be messy enough. It's not as if the ethnic split is so perfect - even in the Crimea alone, many of the ethnic/linguistic Ukrainians and, as I understand it, especially the Tatars would be radically and perhaps violently opposed to such an annexation. In the East as a whole, we'd be talking about a minority of several million people who have little or no desire to join Russia, even if you assume that all of the Russophones do want to join Russia, which seems like a stretch to begin with (I read a couple of days back that the mayor of Kharkiv declared, unlike the leaders in the Crimea, that he accepted the authority of the Rada).