1 / I don't have my Jepps with me, so I cannot quote line and verse, however, there IS a paragraph which states the contact PHONE numbers to ring if comms are otherwise unavailable. Dunno how the pax will treat you if YOU tell them to turn off THEIR fones, but use yours onboard!
2 / Also, I believe that an IFR flight can get airborne and contact centre/flightwatch etc BUT remain within the boundaries of the CTAF until comms established.
3 /
Assuming hypothetically it is full cloud day, (ie solid) IMC 300’ ft AGL off the ground
I would presume that you DO have a ground agent in this case as you would have to be a two crew turboprop , autofeather equipped.