The game is essentially a standard idle game until you die -- then honestly it's pretty painful. Your ability to survive a floor gets cut in half, then a little bit less than that since your clicking is divided. But the only way to rejoin is to beat the same level that beat you. Which effectively means, grind as two solos until your individual levels are almost doubled. Then you'll be back to where you were before you died. Which, incidentally, is still weak enough to die.
Getting separated is too harsh a punishment. It'd be one thing if there were some advantage to being separated, such that it would be easier to rejoin, or each person got more experience per kill. But as it stands, it is essentially a run killer.