Will be curious to see what they do with the next/last season. They're going to need to (or darn well
should) grow up (or finishing growing up) fast for their own good and leave behind any childishness they still had room for when dad was still around. (Looking at you in particular, Mikey.) They may be quite capable, but there's surely still ways they'd feel kind of lost without him. Agree and do hope he turns up in some spirit form.
I suppose if they need a parental figure there's still April's dad, but that guy isn't good for all that much. There is Casey's dad who we've never ever met. Though my vote is an Ancient One to watch over them for a while and continuing training, but with only one season left that intends on not being so serialized... Maybe not.
'Course, I suppose he could be the one to introduce them to some kind of interdimensional stuff that brings them across Usagi, like how 2003 meet him at the tournament.