2 Timothy 1:16

The Lord grant mercy unto the house of Onesiphorus: for he oft refreshed me, and was not ashamed of my chain; but, when he was in Rome, he sought me diligently, and found me

The house of Onesiphorus ... This plea that the Lord would grant mercy to this man's house seems to imply that mercy had not been granted to Onesiphorus; and, from this, many have speculated that he had already been put to death, but there is no way to be certain about this. It is just as possible that Onesiphorus, like the apostle,, had been imprisoned and was awaiting execution, and that the mercy Paul hoped would be extended to his house would be that of their not being arrested and charged similarly, that is, mercy from Nero's persecution. The latter view of course would explain the omission of his name in Paul's plea for mercy "for his house."

It is idle speculation to dwell upon the long and diligent search, through many frustrations and dangers, which Onesiphorus conducted before he found Paul, or upon the manner of his refreshing the apostle, etc. True knowledge of all these things has not been given.