The end of all suffering. Death is the answer to the multitude of problems which encompass life. The ultimate answer. To me, there is no downside. How can there be? Death is the wonderful end to it all.
It's a pity you feel that way, but I certainly don't. I agree with the 'end of suffering' part, of course, as long as there's truly no other optioin, but I don't see it as an ultimate answer to the 'multitude of problems'. I think LIFE is the answer to that lot. Standing up and fighting your corner as long as you can. And then, only then, when it's really not possible (as with me) to go much further, choosing death as the only way forward.
The downside to death is that for some reason or other we came here to live. We didn't come here to die. Not logical. Most of us aren't given a Disney fantasy role to play, but we have to make the best of it that we can.
For me, life is like going to school. You'd often prefer not to go, but you (hopefully) make pals, and have good and bad experiences, so on the whole you're glad you went. My school experience wasn't that great because of a medical thing, but I still look back on it quite fondly and wouldn't want to choose to erase it all, the good nor the quite many bads.
In short, the downside is that death can be too easy (as an idea, not so much in the practical sense) and convenient, UNLESS you absolutely have reached a point of no return (like me) and it becomes a viable, logical, rational and unemotional action.