Missable Collectibles

I think there are a few things that are inexcusable if found in games today: getting stuck with no way to progress (I haven't had this happened since King's Quest 5), not having the game autosave somewhat frequently, and collectibles that can be missed with no way to get them without restarting the whole game.  There is nothing more aggravating to the Collector then to finish a game with 99/100 of something, especially if there is no way to go back and find that last thing.  This should be avoidable for any type of game.

For an open world game where players are free to explore, then either players should be able to return to any previous destination at any time or if that doesn't make sense (some area got blown up or otherwise destroyed during the events of the game), then any lost collectibles should be moved to a new location.  Some games have made missed collectibles purchasable, which is a fair trade-off.  You didn't explore well enough and missed something, so you literally have to pay for it.  Otherwise, just find some way to put them in another area or allow the player to time travel back to that area before it was destroyed.  This may be a challenge for the writers to make a non-hokey method of doing this, but I think it's worth it to keep gamers happy.

If the game is level based, then the main menu should give an option to replay a level so that players can go back and get everything.  Even more important is that the level select menu should say how many of each collectible is remaining in the level or at the very least say whether there are uncollected items left or not if you don't want to give away the quantity.

These rules don't just apply to in-game collectible items, but achievements as well.  There is no good excuse to have achievements that players can't go back and accomplish after finishing the game.  That's only going to make upset players when they have to begrudgingly replay the game to get them or be annoyed by having 99% completion.  Wouldn't you rather people replay your game because they want to?