Can a life estate be revoked if the life tenant moves to a nursing home and the current tenant refuses to pay expenses?

Probably, given the cited circumstances. Some life estates are "determinable" meaning it automatically ends upon the occurrence of a specific event, other than the death of the life tenant. There are also those which are "condition subsequent", meaning the land is granted for a specific purpose, such as farming. A life estate can also be given to the life tenant for the life of some other person (estate pur autre vie). One of the constants of a life estate is, the tenant(s) cannot squander the property and must pay all expenses, taxes, utilities an so forth, unless there is a directive that states otherwise. The biggest factor obviously would be, if the person is a named life tenant and therefore has occupancy rights.