I think it would be a bad idea to merge the marine and the paras. Both have their own deployment method (the paras need to focus on air assault more than airborne which is frankly obsolete and only an emergency method of deployment now)In responce to earlier posts, I was in a Parachute Artillery regiment and very much a shoot and scoot, but that was then. I think Drones will take over most of the tasks we used to train for. However to answer the originating question I see the demise of the Parachute unit. Whereas Paratroopers do remain highly motivated and excellent shock troops, I cannot see a future for Brigade or Division sized Airborne formations. There will still be Parachute capabilities but on a small team basis. In Britain I see the Parachute and Commando brigades merging within my lifetime. I could also probably make a case to get rid of the Guards Brigade and Battleships.
The Royal Marines have become alpine specialists, the paras need to add an environmental specialty like desert warfare.
Both units remain an elite.
Drones (or more correctly UAVs) won't take over the function of a battalion sized artillery fire mission. hey are tremendously useful but there's a limit to the amount of ordnance they can carry.
The British Army will never disband the brigade of guards - it's only an administrative grouping anyway - though I can see the number of foot guards battalions reducing with perhaps the Coldstream and Welsh guards regiments having to merge with the other three.
There are no serviceable/commissioned battleships any - the RN hasn't had one since IIRC 1960 when HMS Vanguard was retired.