what happened to all my collections i had bought

You would download it from your purchase history. https://support.xbox.com/en-US/xbox-360/store/redownload-content

In the rare event something has been completely removed from all of the servers, you do lose the content if you did not have it downloaded already. And no you do not get anything in the event that happens. Its part of purchasing digital licenses. Content
is not removed to make room for server space. Content is delisted due to lack of sales, publishers losing licenses, things like that.

Say all this did happen with the new Xbox...... What would happen if your console became faulty and had to be replaced!? Would your games collection then be useless!?

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Hope it doesnt happen even though i buy new 99% of the time

Same for me, but I had bought some of the personalization packs on my xbox 360, then I upgraded to xbox one, and now they won't show up. It says I already purchased them and "You can get this in the apps and game collection" but nothing happens when i try
to access them in the apps and games collection.

I also had this happen to me yesterday. I was so upset. 46 red and all my unlocks, collectibles....gone! Can I get some help!!!!

Only games that are backwards compatible will show up for redownload. Not all 360 games are backwards compatible (like the ones you listed). You can see a list of backwards compatible games here - www.xbox.com/.../backward-compatibility