I find it hard to believe that the co-op’s rules state that if you are only “a few weeks late” they can begin the proceedings to revoke a member’s shares. However, even if that were the case co-ops are (quite stupidly) governed under the District’s (assuming this is DC) landlord-tenant laws. So if your friend was behind enough and the co-op wanted to pursue revoking the shares and claiming the unit, they would sue in Landlord-Tenant court, and let me tell you from personal experience that it is a herculean effort for a “landlord” to win in that court against a “tenant.” The courts bend over backwards for tenants, and assuming the co-op won, the member would literally have up to the minute the marshall’s showed up to take possession of the unit to pay up in full.
That being said, the best way to avoid “eviction” is simply to abide by the rules and pay monthly fees as they are due. Most co-ops have in their rules methods and processes for dealing with delinquencies. Considering how tilted landlord-tenant courts are in favor of “tenants” it would be highly idiotic for a co-op board to go that route if a payment was just a “few weeks” late. It’s really something that’s only done when you’ve exhausted all options and the member with can’t pay or simply won’t.
(Under DC law, when you own in a co-op you own a share of the corporation, but you as a person living in the building are considered to have a tenant relationship with the landlord, the co-op, of which you are an owner.)