sorry for the late reply, been letting other things (like work) get in the way!
As R5oss says, you're a Subaru owner so you're all right!
I can't recall anyone else talking about the oil light coming on at idle after a run with a Subaru diesel...but that actually used to be in the handbooks of cars from the 70's and was OK so long as it went out when the engine was revved again. That was a result of wider tolerances and lesser oil abilities back then. Not sure it applies to any modern engine, let alone a Subaru!
I can make some suggestions further to R5oss:
* I think checking the oil pickup screen (if it exists) is a good idea in this case. I also own a Mazda 2.2l diesel and that is a known issue with those cars- caused by the (very 'clean') oil specification, some oil dilution/injector leak issues and oil change intervals- but by the time the oil light comes on in the Mazda it's too late, the damage has been done.
* Oil light coming on could also be caused by the incorrect oil being used- so it may be a good idea to change the oil and filter and recheck after that.
* With the oil change, it may be wise to send it away for analysis to see what oil was used, whether it was suitable and whether any damage has been done to the engine.
* It will be worth a good scan of the ECU (OBD-II) from a proper scan tool (mechanic-spec I reckon) just to see what codes have been stored in the past, present (they may not have tripped the check engine light) and/or are incipient (have not tripped the check engine light...yet)
* As R5oss said, the engine cut-out on the freeway may or may not be related to the oil light issue. Certainly that type of issue should trip some sort of code or memory store for the ECU...hopefully! This happened to us once on the freeway- the car cut out under acceleration on the freeway on-ramp...luckily it was downhill and it cut back in by itself. Unknown cause at the time but we had turbo hose and other emission control issues and the car was decarbonised by Subaru shortly thereafter...
* ...to that end, if the turbo or intake hoses/pipes are split and/or broken and/or loose it's possible for the car to cut out. May be worth a check esp. as it's relatively easy and simple.
* Given the car didn't restart immediately after cutting out some other things to check are:
- fuel quality
- fuel filter (not clogged and/or full of water)
- fuel pressure, maybe you have a fuel pump/suction control valve problem- I think the OBDII will give you a readout of that (or maybe the commanded value)but it may need a manual (fit a gauge) measurement to see what's really happening
* was the car run out of diesel and it hasn't been primed properly (our had a priming pump in the engine bay mounted to the firewall. If it cuts out it may be worth giving that a go just to see. Check the fuel gauge is calibrated properly- maybe it's indicating lots of fuel but it doesn't really have much.
* was the car stored for a length of time and biology has got into the diesel and therefore the fuel system
* Oil takes a while to drain back into the sump on these cars so let it sit 15 mins before taking the oil reading- this applies when filling it up after an oil change too apparently!
* A clogged DPF will eventually cause the car to cut out but with no DPF light showing you should be OK on that front.
Hope this helps and hope you don't have a more serious issue about to show