"Is a crown a fairly simple thing to replace?"
"Is Diamondlite/Diamondcrown the best or is there something newer and better I should request?"
There are now multitudes of all porcelain crowns. You might ask your dentist what he has seen the best results with. Depending on technique and the lab he uses, there are a variety of good options.
"I'm a bit bummed that this only lasted 5 years but considering I had something like 10 teeth done, maybe that's still pretty good odds. And maybe it's my fault because I chewed ice a few times and I'm pretty sure that's one of the top dental sins, right up there with opening beer bottles with your teeth."
You are correct, chewing ice and opening beer bottles is horrible for your teeth. Porcelain is really strong, but also very brittle, these habits can extremely shorten the life of a crown (average 7-10 years for decay, 10+ for the porcelain chipping off like you mentioned).
One other thing you can do is ask for a nightguard. With every patient I have with multiple crowns I suggest them. A nightguard is a plastic covering for your teeth that protects your crowns and teeth and greatly increases their life. A nightguard (if worn) is like insurance for your teeth and crowns, they are also fairly cheap.
"I would imagine the enamel is gone though, so won't it start rotting without a covering? I would love to just leave it alone, but I don't want it to rot away."
Most likely you broke the outer porcelain layer and not the base layer. This means your tooth is still protected yet not functional. If this base layer is completely intact, you will not rot the tooth. However, without function your tooth will move over time out of position.
"I'm really torn between going to the good dentist, going to a cheaper dentist, or just leaving it alone and waiting. It seems to work ok and since it's on the top and the very last molar it isn't hard to clean."
Depends on your definition of a good dentist. If you think he is good because he is expensive, I see no reason to go to him just for that. If you trust him I would absolutely go to him because there may be several options (mostly timing).
Temporarily, you can have the porcelain smoothed to prevent tooth damage and help prevent more fracturing. However, if a significant part of the porcelain has come off, the crown does need to be replaced. I would not wait to go get an opinion.