I know a little about UAE law (I work in law in the GCC, just not UAE). The bank is able to be unflexible if it wants to be and default is a criminal offence (although this is being reviewed at the moment - it may change). You need to find some UAE lawyers who are prepared to sort out the mess for you but no one is going to be able to 'negotiate' with the banks.
Personally I'd recommend him staying out of the country until this is sorted out. Them issuing the arrest warrant does not mean that he will be successfully prosecuted but he will be arrested and, even if released on bail, will not be able to leave the UAE.
I doubt the lawyers are refusing it because the bank is government owned. The lawyers will be refusing because you have limited chance of success and they have concerns about getting paid.
They may or may not pursue through the English courts for 100k (I assume GBP not AED). Depends a lot on what assets you have that they could claim again i.e. whether it makes commercial sense to do so. If you have no assets in the UK advice to the bank would usually be to not bother as a judgment in its favour costs money but doesn't actually achieve anything. This assumes they wouldn't do so out of principle.
If they do push English court proceedings, I believe a court will allow you to negotiate payment plans post judgment but check this. Also note that you will most likely also have to pay the costs of the legal action (again check with somone who knows English law) which may be substantial. You are much better, if at all possible, trying to find a way to get hold of the money to pay it off here.
Basically, you owe 100k and need to work out how to pay this. The bank can negotiate on payments but it doesn't have to. This is not nice and this is not a good situation to be in but you need to face it.