popay
Strictly speaking, ATC should revise the cleared First Stop Altitude if an amended clearance is issued whereby the aircraft is required to fly off the SID immediately after departure.
If they don't, then the flight crew really ought to seek confirmation from ATC and challenge the response if the First Stop Altitude doesn't permit the flight to comply with MSA (either published or as per company SOPs).
MSA would be the safest choice of a revised FSA if ATC doesn't offer an adequate alternative - not final cruising level.
Turning right without informing ATC - albeit in VMC - is dodgy because the crew may not have full situational awareness of other potentially conflicting traffic.
The fact that R/T contact with ATC (to advise them of intentions) couldn't initially be made, simply exacerbates the potential for a safety-related incident.
Hope this info is helpful - you don't say whether this airspace is a radar or procedural environment, or whether if radar, ATC is equipped with primary and secondary radar, or just primary. Obviously, if it's a radar environment with PSR and SSR then ATC can at least see what you're doing and where you're deviating from the revised ATC clearance.
In summary - best advice is "If in doubt - before take-off SHOUT!!"
