What do you do...

At extreme volumes there comes a point where I cant hear anything anymore without earplugs. It turns into a big mush and is like being underwater.

Do y'all have that one guy who just won't use hearing protection?

My ears are bothering me just thinking about this.

that one guy was me till about 5 years ago...I am a dumba$$ on many occasions!

now it is just the lead singer

and yeah, it does become a wash of guitar and cymbal basing static ater a while. The headphones definitely help that
I'm going through this and a whole plethora of things are against me......
Guitarist is the founder member, he controls the sound, he is 15 years older than the rest of us and is deafer than the rest of us. We do a sound check with him out front to set levels, then the singer goes out front to have a listen and more often than not reports that guitar and bass are killing the drums (the answer to that is turn the drums up rather than the guitars down) but then he comes back to the stage and I watch him turn his amp up 5 times in the first 3 songs because he can't hear himself. I have argued the case for monitors until I'm blue in the face. We all went out and spent big bucks on proper iem's but I'm the only one who uses them.
The bass player prescribes to louder is better so he doesn't care, the singer often moans he struggles to hear but doesn't want to rock the boat so it's left to me to be the lone voice of distention. The guitarist just ignores me and the bass player tells me to stop moaning.
To those who may say " just quit", I have been actively hunting a new band for over a year......it's not that easy.
When a musician you play with is too loud, and you ask them politely to turn down and they respond by going out and buying bigger amps and playing even louder?

I could empathise, sympathise, share similiar experiences or have a good grumble all of which are cathartic and enjoyable.
However to address your question, in my opinion tell them that when you gig it's the PA that does the work, not individuals speaker cabinets and the moment you do a gig with an independent PA person then they will tell your guitarist to turn down so why not get used to it now.
If your guitarist won't then it's up to you whether or not you can live with it. I've walked away from a band due to a personality clash and for me that was the right decision, you need to decide whether it's a hassle you can live with or not. Reading other experiences here of people having to turn they're IEMs up has me wincing at the prospect of hearing damage, not worth affecting my health to let someone immature/stupid to live out their Rock Star fantasies in the corner of a pub.