Well, "are definitely not counted" is not true. Open ending implies that you can't know for sure.
So, technically, V not dying is just as headcanon as V dying.
Well, in nomad ending i had, V specifically mentions that Victor's drugs start to be effective, and then Panam mentions she has lots of contacts to where they go to help V's condition. Both express confidence that V will manage to find the solution to her condition and thus avoid dying any time soon.
And if we summon a bit of common sense, then we can clearly see how V's body can un-do all the genetic alterations V's body suffered due to presense of Johnny: if Johnny's persona was the force changing genetic code of V's body, then V's persona, in absense of Johnny, can clearly do the same "backwards", and quite in time - considering that Johnny's managed to create the problem in merely few weeks, while V (after removing Johnny) has half a year or so, as explained by Alt.
Johnny was able to do the alteration to a stranger's (V's) body, so then V can do it to a stranger's (Johnny's to large extent) body, too. Even that Johnny was an engram - is actually the same to V's situation post-Alt, as both were in fact soulkilled, just the same. And even physical device would most likely be the same: i presume, when Alt says she can put V's engram back into her body, - it's actually arasaka's biochip which actually is physical device to which V's engram is put back, by Alt. I.e., V post-Alt would have pretty much same "hardware capability" to re-write body's DNA as Johnny had. 100% same, as it's literally same piece of hardware in use.
This is why at least some of endings clearly indicate that V survives. Some others, of course, indicate the opposite. Now which one of possible endings would end up being "official canon"? No freaking idea here. Is it defined already, or not yet? No idea too. Please enlighten me, if there is anything to know. Thanks!