What it seems you have here is the ASSUMPTION that the recently resigned long standing councillor / chair who was fulfilling the role of temp acting unpaid clerk will (has) resign as a Cllr and continue as unpaid Clerk for 1 year and then assume a paid / employed position as the permanent clerk.
Whereas a Cllr may undertake the temporary unpaid role of clerk in an emergency or between resignation and recruitment, paid officers must be appointed on merit and there should be a properly constituted recruitment selection process.
If your 30 year Cllr cannot manage the unpaid acting job in the interim whilst the recruitment process is initiated then probably best to thank them and let them be on their way.
De facto what is being proposed here is that the PC pay to qualify somebody that may not even be selected for the permanent position.
Has the post be advertised?
How can you be sure there isn’t an already or better suited candidate out there who is better suited to the investment??
You can’t just assume the old guard is a shoe in for the job.