Painting those bricks also stakes a claim to psychological ownership of the location that extends well beyond your lease. If your mural gains enough notoriety, it won't matter who takes over the space after you're forced out. If they keep your mural up, they'll be known as coattail riders. If they take it down they'll just be the jerks that wiped out a vital piece of the community. Nice Guy Eddie's on Houston Street had one of New York's most famous bar murals, a portrait of KISS in full makeup, beckoning you to come in and drink booze. When that place went out of business, it didn't matter who came next, or even whether Nice Guy Eddie's was any good in the first place (some people liked it, some people didn't). No matter what, the dominant conversation was always going to be "I can't believe those a-holes took down the KISS mural."
In the end, as Faust pointed out, somebody's probably going to decorate your wall whether you like it or not -- and taggers are less likely to do their thing when it means desecrating someone else's work. Take control of the message, and no matter what your artist throws up there, you'll be telling people who love drinking that you'll be around for awhile.