Assuming time travel will exist...

The only possible time travel right now is as we are doing it currently. Some time in the future it seems possible to step ahead a bit, but there can NEVER be return.
Enjoy the trip to the future you are currently making.
I am sending this answer to you from the past.
So will anybody else, but maybe mine will be further in the past than others.

Nope, Steve's answer is older.

Hello Dave, you sound very paranoided.

Firstly, let me tell you that Stephen Hawkings, one of the greatest physicists of all time does not believe time travel is possible.

Secondly, if it is, then there is no point worrying about it :)

Well, they wont be able to change the past---as the Grandfather paradox is bogus, They simply will find that they cannot do anything that will change the past enough that it would effect their initial departure time of their time trip,

Bogus?---Yes. a paradox cannot occur across time anymore than it can happen in our own time frame. Ever see an electric relay switch wired to shut itself off? ---It does not happen, it only vibrates to "almost off " and back again. What happens when a long train being PUSHED by the locomotive runs on a switchback loop of track?--It does not run through itself, it simply stops. Same thing if you try to kill your grandpa, you would find you could not pull the gun trigger back---as if some kind of "force" was stopping your desired act.---It's not really a "force' but rather a LACK of force--no energy would exist for the final action---like the electric switch trying to turn itself off.