Maybe...if the restaurant is taking reservations until 7:30, even if the park closes at 7 you will be able to have a late dinner.
I have seen ADR times available for after the park closes, but I do not know if it is all year round, or only during busy times. I would try to get the last possible time, then check periodically as it gets closer to your trip dates to see if they've extended the restaurant's hours. I remember last December reservations after park closing were available.
As far as the Osborne Lights, last December the lights stayed on for at least an hour after the park closed. If there is a Fantasmic scheduled at park closing, they will stay on even longer because many people go see the lights after the show ends.