Paging Woody125
Russian airport lounges are not open 24 / 7, and most certainly not overnight.
The S7 lounge at DME closes when the last plane leaves, usually the red eye to Siberia.
That said OVB is S7's home base, and the Lounge in Novo is way nicer than the one at DME. Complete with a piano as I recall. Quiet and never crowded.
I could be wrong, but I think you better find a place to spend the night near OVB.