Well, I just cut down two monster 'Rozanne' geraniums, dug 'em up and relocated them --in the high heat of summer no less--so I sure hope they'll come back, next year at least!
Anyway, geraniums are very durable in general and many, like macrorrhizum, the big-root geranium, will come back from healthy rhizomes. Cutting them back won't kill them. Spraying them with weed killer will, though, so you'd have to be very careful with that.
