As Illuminator already pointed out, many apostles were still alive after 50 AD..
If you're looking for more reason to trust Ignatius, Polycarp, Bishop of Smyrna, commends him (and his letters) here:
"The letters of Ignatius which were sent to us by him, and others as
many as we had by us, we send unto you, according as ye gave charge;
the which are subjoined to this letter; from which ye will be able to
gain great advantage. For they comprise faith and endurance and every
kind of edification, which pertaineth unto our Lord."
Polycarp to the Philippians (Lightfoot translation)
And of course Jesus commends Smyrna here:
To the angel of the church in Smyrna, write this: " 'The first and the last, who once died but came to life, says this:
"I know your tribulation and poverty, but you are rich. I know the slander of those who claim to be Jews and are not, but rather are members of the assembly of Satan.
Peace!