Any aspects of UK property law specifically about pubs I don’t know, but from having researched domestic leasehold for both personal and professional reasons I can tell you:
At the end of a lease, the property reverts to the freehold owner.
As for being entitled to any money back / the 'deposit' aspect, no there’s none of that. And a lease with no time left to run has zero resale value.
Usually for residential property you would be unwise to consider a leasehold less than 100 years. Below 80 years most mortgage companies would not lend on it.
There's no incentive for the freehold owner to extend the lease – the incentive is very much for them to allow it to expire.
As leaseholder you do get some legal rights to extend your lease – which rights you have depend on the property type, how long you've owned the leasehold, how long it was leased for in the first place, among other issues. Extending the lease is done through a solicitor. However, the cost of doing so typically runs into the thousands of pounds and, crucially, rises exponentially as the lease term runs down.
Fundamentally, with leasehold you are purchasing the right to 'own' a property but for a finite period. Therefore only very long leases have stable value and could be considered an asset in the property market. Short leases are cheap because they are effectively a depreciating asset, and the cost of extending them is rising as their value is falling.
How this applies to the economics of leasing a pub, whether the term / cost / ground rent are normal for the pub business, and whether this deal is good or not, are out of scope for this answer; but in terms of addressing your concerns about the nature of leasehold I hope this is helpful.