Nickeloden (and it's parent company) own the 1991-94 episodes of Doug and can air them at their discretion - I know I've seen them on the Nicktoons channel before.
If this changeover did happen, and I wouldn't be surprised - GAS seems to be completely on computer automation at this point - Legends will probably have a spot on the lineup. It's become one of the signature "classic Nick" series, particularly among college students and young adults, which is probably who they'd be targeting this network towards. Double Dare would probably also return, at the very least, in terms of game shows. The three most-remembered game shows from the Nick era are usually DD, Legends, and GUTS, so they'd probably be the three that remained, at the very least.
The channel will no doubt start off with an extremely diverse lineup of pretty much everything that fits the channel's image (pretty much every show they own), then they'll start adding and removing until they get the lineup they want. If they DO air What Would You Do, record it, it might not last forever.
They almost assuredly won't lease anything - at least unless the channel starts to become successful, so don't expect to see You Can't Do that on Television, David the Gnome, or anything like that. It could happen, but it probably won't.