Question: Does the Greek text of 2 Tim. 1:16-18 imply that Onesiphorus had already been dead by the time of writing these words?:

> 
> The Lord give 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 out very diligently, and found me. The Lord grant
>  unto him that he may find mercy of the Lord in that day: and in how
>  many things he ministered unto me at Ephesus, thou knowest very well.
> 
> 
>

Answer: 
I think that we need to understand firstly that Paul is contrasting Onesiphorus and his household with those people he mentions in v14. He is commending them for their care of him. 

The fact that it is just Onesiphorus' household that Paul speaks of in v15 and not Onesiphorus himself suggests that he wasn't there at the time. That might mean that he was dead, or it could simply mean he was elsewhere, after all Paul refers to the household of Stephanas in 1 Cor 16:15 when he is very much alive (just not at home 1 Cor 16:17)

It is easy to read a lot into the term "The Lord grant mercy to" in v15 and conclude that Paul was praying for comfort for the household. But that is not what he says. Notice in v18 he also prays for mercy for Onesiphorus as well and it doesn't seem to me that praying for mercy for one already dead would fit with Paul's theology. Paul is always praying/ asking for mercy or grace for people. Many of his letters open with such a prayer: Rom 1:7, 1 Cor 1:3, 2 Cor 1:2, Gal 1:3, Eph 1:2, Phil 1:2, Col 1:2, 1 Thess 1:1, 2 Thess 1:2, 1 Tim 1:2, 2 Tim 1:2, Tit 1:4, Phm 1:3 

In the end the evidence is not conclusive either way, so it seems clear that Paul presumed Timothy would know the situation, and that beyond our own curiosity the question does not have a great significance. By that I mean that we should not build a doctrine upon this as a key text, or even use it as a proof text for 'prayer for the dead' etc. The ambiguity precludes it's worth to that end.
The text provided in the question is an accurate translation of the [Greek text seen here](http://www.scripture4all.org/OnlineInterlinear/NTpdf/2ti1.pdf). This does not state that Onesiphorus is already dead, but gives us clues that lead to that conclusion. First, the mention of Onesiphorus' grieving family ("The Lord give mercy unto the house of Onesiphorus"), then the hope that the Lord will grant mercy in that (Judgement) day. [2 Timothy 4:19](http://www.vatican.va/archive/ENG0839/__P119.HTM) says: "Greet Prisca and Aquila 9 and the family of Onesiphorus," once again implying that Onesiphorus is dead, or at least absent. 

We can pause from looking at the actual words of the passage, to look at the context in which Second Timothy was written. Although traditionally attributed to Saint Paul, [most modern critical scholars argue that 2 Timothy was written after Paul's death](http://en.wikipedia.org/wiki/Second_Epistle_to_Timothy#Authorship). Paul never mentioned Onesiphorus in his undisputed epistles, so it is likely that Onesiphorus was a literary construct invented by the actual author of *2 Timothy*. 

Returning to the meaning of Greek words in this passage, the name Onesiphorus means ‘bringing advantage’. When we consider that Onesiphorus is singled out as someone not ashamed of Paul’s imprisonment and was the one person who sought out Paul in Rome, when others had abandoned him, then he truly did bring advantage. Although Greeks were sometimes given aspirational names, the appropriateness of Onesiphorus in this case is further evidence that he was a literary construct and existed only within Second Timothy. Onesiphorus was not dead if he never lived.