Under Section 108(j) of the Transfer of Property Act, 1882, unless there is a contract to the contrary, a lessee can transfer their interest. However, in long-term institutional leases (especially to educational trusts), if the deed is completely silent or does not explicitly grant the power to sublease, doing so without the express written consent of the original landowner is a breach of lease agreement conditions and illegal
Any agreement the trust makes beyond the remaining 10 years is void ab initio (legally invalid from the very beginning). Once the original 50-year lease expires the land legally reverts entirely back to the original owner (or their legal heirs), the new party would be considered an illegal occupant/trespasser after year 10 and the owner has the full right to initiate eviction proceedings.
If the trust wants to sublease the property at all, it can only do so for a maximum of the remaining 10 years, and even then, they should ideally obtain the landowner's explicit written consent to avoid litigation regarding the nature of the "educational trust" purpose.