Batboard

Can an HT1250 or MTX8250 or MTX9250 function without a PA (zero power output)? If so, what modifications would be involved with doing this?

Any of the listed radios you posted will 'function', but without any transmit power.

In short, a costly scanner of sorts.

If you wish to TX with it at the VCO buffer output level, then you must add a capacitor from the PA input to the RF output pads, or be cheap and simply 'jumper' it, paying close attention to any voltage that may be on those pads in TX mode, hence, the cap.

The explanation of the VCO buffer is over simplified as many radios have more than this to complete a transmit path to the antenna.

Check the radio's schematic to see if you can perform this mod without problems.