I think the others have just about summed it up quite nicely - you are at an age where 'what if' is a perfectly valid question. If you weren't asking that question, then it would be a little concerning given that you are trying to plan what could be the rest of your life. So much so, that it is a question that they even ask during the interviews at OASC - what will you do if you aren't successful?
However, it is also something that the recruiting process will be able to spot a mile off and could count against you depending on numbers, competition etc. Then again, I know of individuals that didn't even consider the military until their freshers fair at uni and happened to stumble across the RAF stand whilst waiting for a gap to open up at another stand! And they are now flying. So it can be done, don't worry too much about the 'what ifs' just make sure you can justify your actions if you do decide to apply.
As for service life, it's a pain in the arse. We're underfunded, undermanned and under-resourced. You will work long hours for an ok-ish salary (I say ok as you would earn a lot more in civvie street for a comparable level of responsibility) and as the RAF gets smaller, promotion chances get slimmer and slimmer. You will get sent away on ops - frequently - and people will try to kill you. When you're at home, you will think your in-tray couldn't possibly get much higher and your boss will show you it can. You will go home frustrated, tired and annoyed because you will have to repeat it all again tomorrow.
And then you'll smile and remember what it is really about. And it isn't promotion, getting rich, sucking up to the boss in the attempt to get a better report to try and get promoted this year.
You remember that you have some outstanding mates who will dig you out of the **** regardless of the circumstances - I had a huge lump in my throat on my last dining out when one of my best mates told be he didn't care if I was under fire, if I needed to be rescued, he would put his cab in anywhere to get me out - you won't get that in civvie street.
You think back to when you were under fire and wondering if this was it. And then you remember how alive you felt when you were on ops, that you were doing something that mattered - screwing up your secondary duties or filing your security paperwork late really doesn't matter in the grand scheme of things.
You think back to the time you went on AT, and a bunch of you stood at the top of a ski run, looked down it and all the locals going down it. And then decided that the black, off-piste, up-to-your-waist powder looked more fun, and proceeded to try and kill yourselves doing that whilst the locals looked on wondering what planet you were on.
And there will be plenty of happy hours that last well into the small hours - the Doc really wouldn't approve of such hijinks as binge drinking isn't good for you. Until you tell him to wind his neck in and get another round in.
Oh and if you can find another job that gives you 6 weeks leave for an equal amount of money - can you let us know???
In short, it's a pain in the arse. When it sucks, it really sucks. It's probably 10 times worse than anything you will get in civvie street. But when its fun - damn its fun and is probably 100 times better than anything you will get in civvie street. And that's probably why the majority of people on this site go home every day and grumble, moan and complain, and then get up again every day to go back and do it all again!