If your country can't supply the new passport in due time, they should issue a written statement to that extent, which you could then show at Immigration, I guess.
First, the Thai government pension is the SSO pension? That is only a max of 3,000 Baht a month.
Secondly, most countries allow pensions to be paid only to persons staying in the country, not abroad. So then there is no need to show a proof of life.
No exit flight or further flight and you wont be let in. The immigration are civil servants, not social workers, so sorry. But there is the chance to find a very cheap flight, that will qualify as continuation. Check the web.