Thanks to everyone that chimed in with their opinion. As the OP, and my first post I might add, I never expected such a response!!
Perhaps a bit more clarity is in order here. For my scenario, let's assume an IFR departure from 0B1-Bethel, ME with an initial clearance from TRACON cleared direct to KLEW (as filed) maintain 5000. Although 0B1 is in mountainous terrain, departing 0B1 to the southeast towards KLEW is moving away from terrain and 5000 is commonly issued/approved because it is such a short flight and is above the MVA in that direction.
Assume that while en route, the pilots asks for the RNAV RWY 4 approach into KLEW and the controller says to expect that...moments later the radio dies and you are in IMC. For argument sake, perhaps in real world, the controller wouldn't say simply to "expect that", he might say to 'expect that' with a vector heading toward SUMNA / when able cleared direct SUMNA or something like that...I don't think it changes the discussion much as my real question is about the altitude. I know from previous experience that ATC will keep me at 5000 until I get closer to the IAF and/or until I get established on the approach and are cleared for it---to descend to the published altitude. I am quite sure that 5000 will keep me clear of obstacles for my route of flight, thus the routine 5000 clearance often given.
My concern is more general - for locations that I do not know. ATC cleared me for 5000 with 'expect the RNAV RWY 4 approach' before radios go out. Whether they descended me from 10000 or I was at 5000 all along, the fact is that I'm entering (or inside) a TAA when the radios go out. I agree with those that said that in this scenario, I am no longer receiving vectors and therefore no longer afforded the convenience of flying at MVA or thereabout. My inclination would be to immediately climb to 5800 to SUMNA if between 30-12nm from SUMNA as stated in the TAA. If I'm greater than 30 nm from SUMNA, since I'm no longer being vectored at 5000 and not on a published route, then I should climb to at least 6500 OROCA (or 7000 for IFR-Eastbound) until 30 NM from SUMNA, then drop back down to 5800 until 12 out and then down to 3100 and so on.
Someone mentioned about never getting in legal trouble and I tend to agree under the circumstances - I was more concerned about what is "safe" and expected by ATC and the regs.
Am I thinking correctly here?