... more than a billion years after the sun burns out. Could mankind survive that? If so, and if mankind were even still recognizable as such, this slow motion event would not present a challenge.
The sun is getting hotter with age. The oceans will evaporate in one half to one billion years from now. No stars actually collide in a galaxy collision anyway, any more than they do now. But it will result in a huge star burst—all the dormant gas being converted into new stars suddenly, and then no more after that.