Alcohol is detrimental to your brain. Cold hard fucking fact.
Together I wouldnt say much happens to tell you the truth. Alcohol inhibits many connections in your brain and I guess the SSRI might have a weird time interacting with the axon-liquidation.
SWIM would say, without extensive knowledge, that together there is nothing extra that kills your brain or anything. Possible serotonin neurons becoming inactive faster due to the excitation then depression with alcohol.
SWIM has a notion zoloft is a really scruffy anti-d and modern ones are much better (but every brain is different and there is no hard evidence of different SSRI effects, but they DO do different things).
Longterm SSRI will mainly increase your serotonin tolerance, which I guess with depressants could bring your S levels down to sub-normal below threshold points. In that effect, alcohol could offset that and make you grumpier while intoxicated and have worse hangovers (which SSRIs can help to soothe). But harmwise, I would say your not doing much else to your brain.
SWIM drank while on SSRIs and felt really normally drunk and had no bad experiences

best of luck. But SSRI meds say do not consume with alochol, maybe someone else with provide the facts.
*** actually SWIM has a notion that SSRI can actually make you drunker... or make you feel as not drunk so one drinks more. One of those effects. SWIM would theorize without prior facts that SSRI would push more signals, which in an intoxicated state would increase effects of drinking. The extra stimulation with inhibition could have a push-pull coupling effect :/