It's not really anything other than someone's death. It's more 'these wishes are safe and will work out how you want'. Anything beyond those, the DM is encouraged to respond appropriately. In 5th edition, there is actually very little that is listed as safe to wish for. In 3.5 the list was short but highly useful. In 2nd though, there were NO explicitly safe wishes. Anything could backfire.

If you wish for a reasonable outcome that's not on the safe list, you should get it without too much trouble, but if you wish something that's grossly unfair, then you get what's coming to you when it backfires.