Fabulous and fascinating. Question is whether earth can survice the onslaught of existing human activity in next billion years rather than collision from next 4 billion years.
Oh, and live will be gone on earth anyway, AFAIK in about 1 billion years when the sun has become so luminous that the oceans on earth will vaporize and ultimately escape into space. And the collision between the galaxies will very likely have no immediate effect on our solar system due to the vast space between stars (and therefore planets).