Leasehold Improvements as per Indian GAAP

"22. The lessee should, in addition to the requirements of AS 10, Accounting for Fixed Assets, AS 6, Deprecation Accounting, and the governing statute", in the books of lessee.

This means all subsequent improvement will be treated according to that standard; to capitalise or not. To answer your second query, the life of asset is depreciable life as the fair value of the lease considers residual value.