I would argue yua being now 5 or 6 years older than MC as she arrived sooner would be a bigger deal in terms of maturing and changing than the 10 years now.
All these girls apparently werent interested in other guys before the MC arrived so i wouldnt be too concered about that (even when it would be reality and no avn-harem lol). It seems not unusual for people in this story to not give a fuck about dating and focus 100% on training which gives the whole thing more leeway anyway.
You excluded quite a few girls already so who are we even talking exactly?
Yua wont move on, never ever, she would already have done that when she was there 6 years alone if she would be inclined to do so. Layla is dead, and swordgoddess with mc whoever he is atm, same with demom princess probably.
So there are kinda only Dyna and Liana left, are you only talking about these two? Liana is a bit of a special case due to being from earth too and her character seems established and scholary. I guess Dyna could move on? But maybe she will just do what she did before MC arrived (aka have fun with girls) so that would not be much of a deal either way.
And well, MC is not just "some guy" who they met for a while and who died than, even to the ones without personal connection to him. He defended them all against a attack which would have possibly eradicated their entire order, hes a legend already.
Furhermore it gives me hope that we will quickly skip usually annoying the "will they, wont they" with most of the LI's and all of them experienced loss and grief now and are more aware of what it means to live in the present.
I throw my desktop out of the window if we get antother "I wanted to tell you something ... I lo- *interruption* nevermind" after he comes back