You may want to check to see if your laser beam are aligned properly. My sensors has a small light on it. If the beam is aligned properly, it will have a green indicator light. It will have a amber light if the sensors are not aligned properly.

Yes, as Hitefox said it is possible that the sensors have become misaligned, preventing them from seeing the signal. This can be fixed easily, but it may also help to have a professional do a full inspection.

The IR sensors can go bad. Not a very common problem though. I'd check rough alignment first, then inspect the wiring (it's exposed wiring so many things can bump into them). A pair of sensors is pretty cheap, but if all of a sudden your garage door refuses to close all the way it could be what's going on

Sadly at some point it might go out of alignment.. But i've had mine for years and never noticed a problem thus far.