what would dimitri do?

Yeah I think so. I mean, he was willing to protect her when she was about to be taken away for "murdering" the Queen. I don't think he's done protecting her just yet; if Rose was convicted for murdering the Queen then that would mean death and we know that Dimitri still loves Rose, his actions are proof of that and I doubt he would want her to die. Same goes for Adrian, Lissa, Abe amongst others; Rose has A LOT of people that love and care about her therefore would do anything in their power to get her out of prison.

I'm pretty sure Dimitri would have went after her to stake her.
I mean ... if everything in Shadow Kiss went down exactly as it did ... the only difference being that Rose turned Strigoi and not Dimitri ... I don't see any reason he wouldn't have gone after her.
They'd just professed their love, made love, and decided to be together and I think that if Rose had been turned or even just killed, he'd have probably lost his control that he tries so hard to keep in check ... which would lead him to go stake her.
Plus the whole convo from VA from the back of the van would have came into his head just as it did Rose ... and there's no way he could have just shrugged that off.
As for him going all the way to help her now ... in Last Sacrifice ... I think he will.
He already proved it by defending her when they took her.
It may take him a little longer to act because of all of the mental issues he's going through, but I think he still loves her with everything and he'd do anything to help her ... no matter what.

yes he would. he'd go out of control and go stake her

yes yes dimitri would!