That depends on how you define permanent damage. Drinking a bottle of whiskey at once will damage your liver, but it will not be noticeable if you only do it once. Same goes for MDMA+alcohol. You might do something stupid and hurt yourself though, as lots of alcohol and lots of MDMA mixed creates blackouts and loss of control, among other things.
I think if I did 400mg of MDMA for my first time I would end up calling an ambulance on myself or my mates would call one. Not because I would be in grave danger - though body temp and fluid intake would need to be very carefuly monitored - but because I would look like I could drop dead any minute. 400mg completely wrecks a person up to a point where it's starting to become a negative experience rather than a positive one. Only you would be so far gone mentally that you wouldn't realise this. Don't do it, I've only done such a dose once by accident (500mg over the course of 1.5h) and while I was OK afterwards I still can't believe how irresponsible I was that night. First aid saw me walking past and wanted to haul me off to an ambulance because I looked like a walking corpse, but I ran into the crowd to avoid them. That was without alcohol involved, if you mixed alcohol with that you could end up climbing a pole naked or something like that, you really aren't aware anymore of what you are doing
I think combining MDMA with alcohol is a complete waste. You will not remember much, if anything at all and the side-effects the next day will probably be a bit more severe. 400mg MDMA is a waste as well, I will never do that again