Board Thread:General Discussion/@comment-27086331-20151017060059/@comment-2112031-20151017100457

The end credits say they died in 2014. Solid Snake was estimated to have about 6 months left to live. The novelisation for MGS4 states that Snake spent the remaining portion of his life traveling the world and living a peaceful life.

Eventually he died with a smile on his face, surrounded by his friends. I think that's a fitting end.