How do you know he can't play this role again? The last manager that played him there was Rafa, no other manager has utilised his full potential as a goal scorer. He may be a bit old but I can gurantee you he can get many more goals there and can still play especially if the defensive duties are taken away from him. Some players go to their 40s, Gerrard is still young.
with Rodgers everyone must press, but it is an organized press not run all over till you die like with Hodgson.
and from what i understand from Brendan's tactics he uses 3 CM players, one anchored in front of the defense, and 2 in the very center of the pitch, they rotate attacking the "hole". it's not like with Rafa where one player was committed to this role.
meaning the old role is not even available, but the new Gerrard will need to do his job AND the Alonso job but with organized switching with the other CM player.
this will actually:
1) save his energy
2) help him avoid injury from overworking
3) extend his career as an important player
4) take full advantage of his long experiencing in influencing both attack and defense
5) teams will have a harder time tracking 2 CM players switching attacking roles