I love this! Reminds me of some of the idle games I used to play on mobile. Hours and hours dedicated to progression (RNG is a bitch a lot of times) but there were side quests and regular boss monster challenges that kept it interesting and entertaining.
Same concept, everyone wanting to fight the boss can do so. Boss monster's health trickling down with every battle (unless it has life leech? lol).
Player units that get eliminated need longer cooldowns or something similar.
Bonus points to the player who can deliver the last hit, killing the boss!