Is an abandoned metal piping system required to be bonded if it is left in place and intact?

If it is in or attached to the building and likely to become energized then I would say yes bond the piping system.

Another subjective item. Key phrase is 'likely to become energized'.

Perhaps the best answer is from your local AHJ.

My interpretation of "likely to become energized" means if whatever the gas is hooked up to uses electricity then it is "likelt to become energized". Once the piping is abandoned, it is no longer connected to anything that could energize it.

It is a situation that we see when replacing services on older residences that have gone all electric to avoid the expense of re-piping leaking gas lines. Southwest construction methods often make plumbing replacement very hard and expensive (no attic, slab foundations)