It is important that you clarify the legal status of the Parish Council in relation to the village hall. You should already hold the documents to confirm this, but it is helpful to carry out a Land Registry title search too. This can be done online for £3.
If the Council is a custodian trustee, holding the building on behalf of the owner (either a local unincorporated charity or an external body such as the Church), the Council has no financial liability whatsoever. It has the power to offer financial support to safeguard the community asset, but no obligation under any circumstances. If you're an ACRE member (and if not, why not?!), they have a couple of useful information leaflets that explain this in more detail.
As an aside, you mention an extension. I hope that the extension is/was built on land belonging to the owner of the hall, or that appropriate leases were signed beforehand. I mention this only as I'm trying to unscramble one that wasn't and that isn't easy to do retrospectively!