Except the mirror would be coated with vapour deposits - ruining it.

Conceivably, the vaporized material could shield the projectile.

It would be kind of hard to fire a laser over obstacles like a mortar. Unless, perhaps, you send up a attach a mirror to a balloon and fly it over the battlefield so you can bounce your laser. :)

The same goes for Katyushas (rockets). Most of them have a range that's well over the horizon, so it would be difficult to fill the same use case with a laser.

So if it were me trying to bypass this system rather than trying to make increasingly complex and expensive projectiles to try and defeat the system I'd just make increasingly cheap projectiles to make it easier to spray the target with them and eventually get some through. The article even mentions that a laser can only point at a single target at a time. To your point if you also target the defensive system you're bound to sooner or later damage the system with one you managed to get through. Seems to me that this system is easily defeated with tactics.