Checking gravity is a bit like a seat belt; most of the time, it's not really necessary, but it'll save your butt on that one time you really need it. I used to bottle and check FG after the fact, from a sample I'd take from the bottling bucket. All of my fermentations had always gone well enough, to that point. Then one day, I bottled a beer that finished at 1.050. That's not a typo. Needless to say, I wish I had checked that gravity before bottling.
Next time you order something, get an extra dry pack of yeast - US-05, Nottingham, something like that. Kept in your fridge, it'll last for 3-4 years, at least, and you never know when you might need it.