What happens if my business doesn't make a return for a VC/Angel investor?

If you have to ask this question, then you might not be ready to raise money this way. In short - if you got money from a VC, you would already know the answer. The expectations/milestones would be pretty clearly defined. However, if things are going poorly, or something bad happens along the way, they may bail early. In any of these events, you may need to buy them out or fold. If they still like your prospects, they may also want more equity, but in any of these scenarios, you basically have two choices - either give more equity just to stay afloat and basically become an employee, or fold and possibly go bankrupt. Ugh.

Angel investors usually get involved - and sometimes cashed out - by the time VCs come along, so their story is a bit different. This is usually a step up from friends/family, but not as cutthroat as VCs can be. These are more strategic investors, and will likely cut you more slack since they have more upside being early stage investors. Also, they typically have smaller stakes than VCs, and it's usually their own money, so the expectations on getting a return are more flexible.

These are just general points of difference, but at least you should now know how these two types of investors differ.