> what do I do if ...
> is it worth it to ...
> How do I decide?
All these are good questions, and you're already doing well by asking yourself these things.
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The first one is easier to answer. If <some option fails>, what you do is move on. You re-evaluate your circumstances, and go try something else. I mean, there's no other way. The alternative is planning something like "If this fails, I'll just become stuck and wither away", which you don't even need anyone to tell you it's obviously absurd.
Many things can -and probably will- fail. We can't know the future and you cannot do much about it anyway.
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Now, the second question is harder to answer. Personally, I would say that education is always worth it, in itself. But then again one particular form of it -i.e. going to this school or choosing those studies- may or may not be so.
But consider that you'll also play a significant role in "making it worth it". The same school, courses, the same class, can be different for different people. I can only say this: If you choose something that needs a substantial investment in money and time, make sure you also invest your best effort on it. Don't do it half-arsed. If you're not convinced and you won't work hard to get the best you can from that education, then don't do it.
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Finally, how to decide. Who knows?
A guy I know can spend even a month or two researching on which trousers to buy. Another one I know just goes in the shop, looks at a couple or three of them, and just picks up whatever he decides in a few minutes. And, being honest, I can't say either of them ends up making a better decision.
Probably it's a balance. It seems like a good idea to think about important decisions that can -to some extent- shape your future, of course. But it also seems like a good idea not to overthink it.
If you want to, you could apply a somewhat organized system. Like making a list of the various options you consider, and writing down pros and cons for each of them, and scoring them with various criteria -objective and subjective-. Note though that this will not guarantee making a good decision, because nothing does. But it can help.
Also consider, when making a decision, that it may not mean choosing only one option and discarding the rest. Sometimes you can choose more than one. Other times you can choose one and later in life turn to a different one.
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More in general, I'll add that you're still young and you have time to try things. Don't worry so much about having all your life outlined now. Try some stuff, re-evaluate, correct and you will slowly figure it out.