Well they DID blow his mask to smithereens, it might've hurt his head? Besides, doesn't that clone stay in that dimension now? Tobi might not dare phase out anymore.
Or they just have to fight at a disadvantage like every protagonist in the history of ever.
maybe saskura will show up with the rest of the fodder 11 and heal kakshi a little bit or naruto may be able to hook kakshi up with some health with his cloak remember how km made yamatos wood sylt grow he said naruto was "teaming with life force " or something like that or maybe he will die
its 3 4 against one. so what if one is tired... the others will back him up to regenerate his power....
plus, while staying back, kakashi can counter more effectively learning the situation more clearly.