A single bent valve makes that cylinder useless. There will be no compression. A worn or leaky valve seat gives you lower compression ratios, as well as worn rings or damaged cylinder walls.
On the Subaru interference engines I have seen with a broken belt ( 1 was DOHC 2.5L, 2 were SOHC 2.5L ),
The DOHC had 11 bent valves and 3 damaged pistons.
One SOHC 2.5L had good compression so we replaced the belt. The owner sold that car 2 years later and it was still running fine.
The other SOHC 2.5L had 1 pummeled piston and all the valves in that cylinder were damaged. In fact we had to replace that head.
So a broken belt can have different results, but the message is, DAMAGE CAN HAPPEN. If it doesn't, consider yourself one of the Lucky ones.
98S, 2014 Impreza 5 dr Ltd (9 Subaru's since 1978, 7 were 5 sp) ILuvSubaru's