Methinks you're possibly asking for advice to solve YOUR own dilema.
If it is YOU, you've only got about a year to push (That's if you are referring to 3 years adult service already served.).........what's wrong with you, GET YER CHUFF CHART UP............................CRACK ON & GET A GONG!!!!
On second thoughts, either YOU or your 'MATE' would probably be a liability on Ops................
Much as I despise the attitude of the individual needing advice surely if he's done 3 years he's due out in 4 years these days - all he needs to do is sign off. The Chain of Command then takes a decision on whether he goes on Ops - clearly if he's already warned off then the above is not open to him. However I do think the spineless sh1te should deploy.
There is no point in trying to bluff depression; he will be sent to a trick cyclist who will be able to tell within minutes whether or not someone is genuinely depressed. And when he is found to be a bluffer things will not get any better for him in any way.
No point going AWOL either, they always find you (I had to deal with a guy who had been AWOL for 14 years once).
Short answer: Soldier On.
Emphasis on being a soldier: someone who is not so jack that he would leave his mates to go on a dangerous tour without him.
If he can't find a spine from within himself, counsel him to take into account the guys who will be left short because he fancied the easy life at home... another soldier having to do more/longer patrols may die because he is so tired out that he doesn't spot the IED that kills a bunch of our guys - all because his "mate" was jack...
He needs to stop thinking about himself and think about others.
Besides which, the tour might make a man of him at last.
Can it be that he actually thinks that none of the rest of us are frightened as well sometimes? The difference is that some of us are men, not mice.
...and some of us are small fluffy animals who need to be tickled daily. Nice to be one with a personal history to be happy and satisfied with, rather than one with memories to be ashamed of, don't you think?
Things are rough out there at the moment, but most people return unscathed.
Look at it this way, a tour of Helmland buys you automatic admission to the big boys club, and the right to hold your head high for life.