Waldy will be offered the Bulgarian crown, and as in OTL he will refuse it. He was the least ambitious of Christian IX's children, and considering that he had a wife who spent her spare time playing firefighter, I can't see that changing.
Yes, he liked the quiet life. Probably for the best in all honesty, although his children were quite impressive.
Princess Marie was a troubled soul, not maternal and stuck in a loveless marriage, she had a lot of sparetime on her time, for a long period while, no man was safe around Valdemar.
Eventually he settled down into a romantic relationship with his nephew Prince George of Greece, which lasted the majority of their adult lives, only a decade separating them in age.