While true that anything traveling at light speed (which, to the best of our knowledge, is only photons) no time passes. But to the observer in a different reference frame, time does pass. So our sun could have exploded 1 minute ago, and we'll not know about it for another 8 minutes. The photons would experience no passage of time, but we would. So a photon could never "decay" because no time elapses in its reference frame.

I'm not aware of any quantum entanglement of photons from distant objects, but if you have a paper I can read...

I did read a while back that communication via quantum entanglement would not be possible. The particles are entangled so as to conserve a trait (e.g. spin), but if you disturb them the entanglement is broken. Measuring them disturbs them. And once broken, the entanglement cannot be reestablished remotely. It was an interesting read.

You may be referring more to simultaneity than entanglement.

en.wikipedia.org - Relativity of simultaneity