They will vote on the ORIGINAL deal (which stockholders already have the information). The only reason to vote on the original deal is if they can't come to a mutual agreement regarding a NEW deal. They agreed "in principal" for a $16.50 transaction for the new deal, but now that they get to the nitty-gritty, it is possible that the negotiations break down. Foundry has effectively set a deadline for these new negotiations for Friday.
I would assume that if the new negotiations are deadlocked, then Foundry will continue and vote on the ORIGINAL, agree to it, and then Brocade will have to pull out and pay the $85mil (unless they've somehow gotten the extra $400mil).
But, if Brocade & Foundry come to a new agreement by Friday, then a new proxy will need to be filed and the vote will be postponed until everyone has received their proxies.