No word on what you can do when the pass expires but normal process would be that you could renew it a the usual premium pass renewal rate for DVC members or change it to a regular AP pass at the AP renewal rate for DVC members. The pass would expire 4/11/14 if first used 4/11/13 and thus will not be usable for a June 2014 trip absent renewal.
Yes, once you exchange the voucher or pick up the pass (with a will-call number), it expires one year from the date. So if you activate it in April 2013, it will expire before your June 2014 trip.