But unloading pflog unload pf as well.
But they shouldn't be dependence, pf should work even if pflog hang or crash (but obliviously disabling logging and wait until it available and report about it)
Pflog as well should report about pf crash or hang.
pflog depends on pf. It's not possible to load pflog unless pf is loaded (or more accurately, "kldload pflog" will implicitly load pf as well). That also implies that you cannot unload pf itself until pflog is unloaded. That's entirely expected.
There's no scenario where pflog can crash without taking the entire kernel down.