Hi,
If it is as your mech says, the idler pulley bearing, then it is absolute NoNo to use, certainly not for long.
Air con compressor idler pulley bearing noise is bad news. Inside the pulley sits the electro magnet for the clutch. The clearance between the coil assembly and the pulley are very small.
The noise is from the bearing usually having become dry. It is a double row ball bearing and the extra friction will cause it to heat up, and when it wears enough it will wobble and the magnet shroud will start rubbing on the clutch coil. This will mean defo replacement compressor. My guess is that if it has got to the stage that the noise is as noticable as you say, it is just about coming up to this stage.
On some cars the clutch can be removed in situ, and the pulley removed and the bearing replaced, but I wouldn't have thought the Omega is one of them, as the two pipes coming up form the compressor turn up just in front of the pulley, and if you have to remove these and lose the gas, then I would have thought that although awkward to remove, it would be easier to take the compressor off to repair. As already said, most air con repairers will not touch this job, because at their repair rates, it costs more to do than cost of an after market replacement unit (Not vX), ie about £250
I have seen them on net for about this.
Generally, you do need some special pullers, but I have found that as long as you have a bit of ingenuity, and small set of pullers and good circlip pliers, inside and outside, you can usually get a clutch and pulley off and back. The special tools make it easier and more foolproof, but some jobs, like changing a compressor front seal, cannot be done without.
The bearings are usually quite oddball dimensions. You will need to go to a bearing supplier, and generally hope he will order it for you. Usually about £20
Untill you can decide what you are going to do, I would get hold of the auxilliary drive belt for the version of your car that is not fitted with air con and fit that. £20 odd unless you can get s/h, I expect there are some forum members that can even give you the part number, but, if the A C idler pulley seizes up, and something like the tensioner pulley breaks, or the water pump shaft gets bent, or the flying belt smashes the engine side cooling fan housing, which then punctures the rad matrix, then you are really talking money and time. I have seen it all happen on a Renault I had.
HTH
Roger