Apple has done this in the past with the excellent iDVD software, which was removed from the operating system on a previous upgrade. Apparently Apple believes DVDs are obsolete - try telling that to a 92 year old relative who wants to see family holiday videos and only has a DVD player and no Internet!
However, in that case at least - and it may well be true for iPhoto too - software that was included with earlier versions of OSX remain on the system when it is upgraded. iDVD was there after the upgrade. For a MacBook I bought after the upgrade, I purchased iLife 11 from Amazon and retro-installed iDVD, though that did have its challenges.
So, hopefully you will find that iPhoto will still be usable after Yosemite is released.
For my part, I'll check that out on my MacBook at the time and if iPhoto vanishes, I simply won't upgrade my iMac to Yosemite.