Selling the pattern makes you a lot of money quickly, selling the cloaks makes you more money but far slower.
After P3 is out, it is likely there will always be the need for the cloak, few examples:
Guilds are progressing through BWL and therefore must have/buy the cloak
People have alt characters that need the cloak
New/Returning players that need the cloak
etc. etc.
Bottom line: people need the cloak.
Of course, most guilds will try to secure at least one of these patterns to have a guildy craft the cloak for them without having extra costs.
Again, the choice you need to make is basically the following:
Do I want a lot of money now?
Do I want a (slow but) steady source of income over the course of Classic?
Whatever the answer to those questions is should determine whether or not you sell the pattern.
You MAY also run the risk of several other also getting the pattern by the time BWL is out, giving you competition in the market.
Like others have said before me, selling cloaks may not yield any income now, but it will have a market once BWL is out.
(same philosophy as with twink items, the market will open up once battlegrounds are added)