If you are right Dez and Duges is there for the long hall, then I can say with some confidence Mary wont be.
I don't think he is there for the long haul. I think once Farrell returns Dugan will be moved back to fullback. I think what Mary is doing is trying to utilise the best available talent for the benefit of the team.
As everyone has highlighted - and I don't think anyone has disagreed - Dugan is primarily a fullback. There are issues with his game as a fullback - again we are all in total agreement. These are basically centered around his passing game and his ability to play a role within a set move. His kick returns should be valuable - but not in this current team. They are being wasted and have not provided any value over the past 2 months.
I think the issue with retaining him as fullback and bringing in, say Charly, is that you have a greater range of issues to work with in return for 0 improvement. So for example, we still have the issues with the forwards, we still have the issues with Dugans passing game and crowding his outside men, and you introduce new issues around adding Charly to the back line (Charly may have defensive issues and definately isn't as dynamic as Dugan or even Farrell).
By moving Dugan to centre and bringing in Quinlan, you are basically adding a quality centre into the team and another ball player. Nobody can deny that even with his limited experience in the position, Dugan is a much better centre proposition than anything else we have available at the moment. He is strong, can bust a line and has pretty good defense.
Quinlan does have deficiencies in the custodian role but he does add another dimension into the attacking line. So in effect, without having to work on the forwards at all, you have improved the teams attacking ability in 2 key areas. It buys time for the coaching staff to focus on the forwards only and at the same time adds fire to the back line that, when it clicks, will be an oppositions nightmare. Quinlan would make a great utility but at the moment there is no room in the team for a utility - and I personally like the 2 dedicated hooker rotation rather than add in a utility player who has no experience in a hooker role. So it makes some sense to have him in the team in a position where his skills and experience can be utilised.
Contrary to the belief of yourself and others, the season isn't over just yet. There is still a chance we can make the 8. It gets slimmer each week, but what I see Mary doing is trying out an option to give him the best chance of achieving that - and you have to give him props for not giving up on our chances of reaching the 8. As far as we know he is only here for 1/2 a season and I think the forwards are too big of a task to tackle in that short period - not to mention potentially the only real solution may be to recruit. This move has the potential for more short term reward.
As I said, I think Farrell is our long term centre and Dugan our fullback. All I am saying is I think this is a reasonable solution in the short term. It may work, it may not. There is no denying that we have seen some improvement in the team over the last couple of weeks and there could be many contributing factors to this (Price gone, Mary's influence, Benji's influence etc). But you can't just dismiss the fact that this change could well have made some difference to the way the team are playing.