If the landlord continues to own the house his financial problems are completely separate to your friends' tenancy of the property and (assuming that they keep to their side of the agreement) they can't be prematurely evicted.
However, if the landlord has a mortgage or other loan secured on the property, and the property is repossessed by the lender, the tenancy agreement would not be binding on the lender. (There are very limited circumstances where that would not be true, but I very much doubt that they apply to your friends' tenancy). See here:
http://england.shelter.org.uk/get_advice/advic e_topics/eviction/repossession_by_a_landlords_ lender
You, or your friends, might be able to learn more about the landlord's financial position by checking the publicly available records. First, check to see if he's been made bankrupt. (That would be extremely worrying because he'd almost certainly lose possession of the property):
http://www.insolvency.gov.uk/bankruptcy/bankru ptcysearch.htm
Then check for CCJs, High Court judgements and fine defaults:
http://www.trustonline.org.uk/
Chris