Even if Romania is not a monarchy the royal line goes on. Lets not make the mistake of confusing a political system like monarchy with royalty, which is mostly a hierarchy of people and a set of written-unwritten traditions. Monarchy is only a part [central, off course] of royalty. They are quite different, even though they usually go together.There is royalty without monarchy and vice versa.
The heir is important and in a situation like this I think the will of the king has a considerable weight, despite the legal frame. I don’t think the Hohenzollerns would dispute the requests of King Michael, they seem to be in good relations. And also Margarita is the only offspring of the royal family willing to involve itself in Romania, as she already does. Paul Lambrino is not a serious candidate [even as a person he is a joke].