Can the smaller Chetaks fit in?
No just wanting to know , since we have 4 more ships on order.
The hangar is about 14m in length. So it can fit in anything smaller than that. So the Chetaks, definitely, with the rudimentary blade folding system designed for it. But it's not advanced enough to be used on ships as a dedicated helicopter.
Since Talwars can can carry only 1 helicopter, I don't think the Ka-27 will be replaced. The Russians also have multiple ships with the same problem of a small hangar, so it's not a problem for the future development of new helis.
Even if we have 10 Talwars, we only need 10 helicopters. This will allow the use of 1 helicopter for each ship at any time, with some being down for refits and repairs. So the fleet requirement is very small and neither NMRH nor NUH have to be troubled by the requirements for Talwar class.