You have lost it all - or at least some part of it. You can likely force the array online, but basically 2 discs are out of sync and Raid 5 can handle 1 disc. Ergo - bad data. how much.... depends on what was going on at the time of failure.
Now, if you lost data then no, you did not loose it because of the 2 discs out of sync. You lost it because of absolute ignorance of something any professional should know: RAID is not a replacement for backup.
As in: In a sensible setup, the lost data would be miniscule per definition because you would just get most stuff back from the last backup. Which may be quite short term (I know companies doing a backup every 15 minutes).
That said, technically you may be lucky and not have lost a lot. I would investigate why - likely write back caching on the discs and a power failure.... so you lost the dirty data on the disc caches.