<i>my car was repaired under the local insurance company authorized shop</i>
But not a Subaru Authorized facility (i.e. a dealer), so thus an independent shop, thus voiding the warranty.
<i>how do I know my car is readily to be claimed "total lost"</i>
It may need a new engine, or enough rebuilding that it would be better to install a new engine. Once you pull the engine, you are better off dropping the new one into a straight chassis, not one which has been in a bad wreck. Leave that kind of stuff to pros like Dale Teague who know what the hell they are doing, or you will have a gauranteed future of problems towards which to look forwards. In my mind the car is toast.
<i>How do I know if my engined is not repairable? BTW, how big is a job to fix a blown headgasket?</i>
Anything is repairable if you have the $$$$. A blown headgasket is a pretty big deal, to really do it right you should probably pull the engine and true the block to you don't end up with another warped head or blown gasket soon thereafter. Your engine was the subject of an impact in a wreck, I would not trust it unless I had it out of the car and blueprinted it, but maybe that's just me being paranoid. But let me ask you this, how do you know the wreck didn't crack the block?
<i>I am still covered by the shop until problems are all fixed so I am not really worried</i>
Do you really want guys who (1) are paid by the hour, (2) are not getting paid for this job because they screwed it up the first time, and (3) screwed it up the first time doing the work?!? Do you think they will fix it up right this time somehow? Will this car ever really run right again? It needs TLC from a specialist.
If it was $10000 to fix it your insurance company should have totaled it.
<i>BTW, if it helps you guys to come up with some thing, I filled my engine with 2Litres of engine oil for about 3000KM milage.</i>
2 LITERS? Your engine only holds 4 liters! More evidence that your engine is probably not going to have a long life ahead of it, in fact is it probably on its last legs. Sorry this had to happen to you.