You can sell a firearm at a substantial profit whether your C&R license is currently valid or not. C&R rules certainly don't prohibit you from selling guns you bought with your C&R. They only prohibit operating as a firearms dealer. Consider two scenarios:
1. You are especially interested in cold-war era European firearms. You see that a wholesaler has Yugo M59/66s on sale. You purchase two via mail-order with your C&R. Upon receipt, you find that one is especially desirable for your collection, however the other is a mixmaster and/or does not help you improve your collection. You keep the most valuable for your collection and sell the second to one of your friends that is also interested in firearms, but is not interested in maintaining a serious collection--he is simply an avid shooter. Your friend thinks that the M59/66 is especially cool looking and the local shops want $450+ for one. You only paid $299. You sell it to your friend for $400. Your friend gets a good deal and you covered your shipping costs on the rifles and have enough left over to add a shelf to your display case. Are you acting as a dealer in this case? Hardly. You are a collector and improving your collection. Making a profit on a one-off sale does not constitute being a dealer.
2. You order a crate of Mosin Nagant M44s for $49 each with your C&R. You rent a table at a gun show in the "collectors" area and sell all the rifles to passers by. Are you acting as a dealer? Cleary, yes. This is not permissible with a C&R license and is clearly illegal. Frankly, this behavior will get you thrown out of most gun shows.
Otherwise, no special rules apply to the guns. Valid license or not, they are part of your personal collection. You may dispose of them as you wish (assuming you follow any other laws pertinent). If your license is currently in force, you must log the sale in your bound book. Frankly, I would log the sale of any firearm with the same information required in a bound book and supply/keep a copy of a signed bill of sale regardless of whether you have a C&R or not, simply to protect yourself.