Yes; Your 30 million baht investment is all gone once your 30 year expires. It's not really an investment, it is paying rent for 30 years up front. In addition, if the land owner dies or sells the land, the new owner is not bound by the lease because it is a contract between two parties and not automatically binding on new owners. It might say that it is in the agreement and it might also say you have an option to renew but the Land Department is not empowered to enforce anything but the basic Land Code provisions and what is registered at the Land Dept and written on the title deed. The Land Dept is not allowed to register the lease agreement or any details over and above the provisions of the Land Code.
This all means that you cannot go to court and get the Land Dept to enforce provisions like registering a new lease for you, based on an option to renew or bind a new owner to the terms of the lease agreement. What you can do, is sue in the civil court for financial damage caused by the other party reneging on the lease agreement. So you have to present evidence of the financial damage, e.g. the cost of new lease. However, if the land owner is dead or is a company that is bankrupt or dissolved, it will be difficult to sue.
Basically lease law needs to evolve a lot more before it is an attractive alternative to freehold, not just extend the time period allowed. However, their are loads of farangs who have chucked away their money signing 30 year leases. I know someone who bought the family home, a nice condo right in the CBD with about 25 years to run on a 30 year lease on the basis that the owner, a prominent institution in Thailand, had given verbal assurances that the leases could be renewed for another 30 years. The units were sold at auction and the sellers came up with that tall story . Friends advised not to buy or accept that it would not be renewable. Anyway the long and the short is that the lease expires next year he is now looking for a new family home.