So him dying at some point shouldn't really have any effect. You can't breath a sigh of relief that he's dead, because he still might turn up and stop you.
Not if your relative pasts are in the agreed no-fly zone. The Doctor and Davros, for instance, have apparently never met in the wrong order. This seems to have been the case for the Doctor-Dalek relationship too since Resurrection Of The Daleks
in 1984, or possibly Destiny Of The Daleks
in 1979. From Remembrance Of The Daleks
in 1988, the Doctor has always seemed to assume that the Daleks he's currently facing are from a later time (for them) than any of their previous meetings. So I think there may have been some sort of accord to prevent things getting too messy. This may well be one-sided, with the TARDIS keeping track of them or refusing to land where a paradox might be created.
(Ten mentions to Wilf in The End Of Time
that there's a causal nexus of some kind between him and the Master and that it needs to be respected. I guess that there are certain levels of interference with Time that can be tolerated and others that can't; an example of the former being affecting things whose outcome or details you have no prior knowledge of, and an example of the latter being any interference that deletes your original motivation to interfere in the first place.)
(Edit: I recall from the novelisation of Logopolis
that the unravelling of the Universe was attributed to the breaking of its causal nexus.)