I've bowhunted for nearly 3 decades now and STILL can't find a need for mechanicals so can't help you with those. But for regular fixed, they are mostly steel and aluminum so they should last a lifetime with the basics of care. Keep them sharp and away from moisture and other than that, there's not alot to them. After you sharpen them you can essentially make them "moisture proof" by sticking them into a large candle to cover them in wax. I know guys who likewise paint theres and I suppose that'd be just as effective. Stainless DOES rust btw, just not as easily or visible so keeping moisture off of them is equally important. I prefer carbon steel vs SS because it's easier to resharpen and put a sharper edge on them but it's tougher to find carbon heads that fly well if you are using a fast vert/xbow.

If your bows quiver has a piece of foam in it to hold the heads then make sure and remove it or try to at least dry it out after a hunt in the rain. That's where alot of guys get into trouble, they dry their broadheads but never think about a wet quiver so they stick them right back in there and that's no different than sticking your knife in a wet sheath!

Keep them sharp, or resharpen after killing a deer if they are not damaged, replace blades if needed. check o'rings or retainer clips on mechanicals. They will last indefinitely if you keep them in top shape.

I have some I have killed a few deer with.

I replace my blades after every animal I harvest or attempt to harvest (aka miss). I want to make sure I am making a clean harvest on the animal. If you use a potential dull broadhead you are taking the risk of having less penetration and also the broadhead will tear the hide and lungs more instead of a clean slice which can cause a bad or good blood trail. Decide sharp or dull? . Another example when you clean your animal do you use a sharp knife or a dull? I use a sharp knife. We as hunters owe it to the animal to take the animal as fast as possible with the cleanest and ethical way. We are taking their life and there is where we should respect that by make sure our equipment is squared away, we are squared away (shooting etc) and we wait for the right shot. I think a lot of hunters tend to not look at it like that and compromise on so much stuff. Don't compromise on something you put so much time and money in to.

I just replace the blades on my muzzys if they look dented or whatnot from an animal/target shooting. Im sure if you used the blades for repeated use in a target they would get dull but once or twice isnt going to dull them any.

Ive had my Muzzys for 5 years. But that may be because I never actually get to shoot anything with them...

Sharpening with arkansas stones
 

...makes me keep them longer. To me a dull broadhead doesn't exit. i'm cheap.
Arkansas stones keep the old broadheads and knives happy.

Spent my younger days getting stuff sharpened.

For ever if you don't us them grasshopper