Yes, obviously. But what you are describing is miners never gaining 95% of the hashrate (because hashers switch to non gigablocks pools), and the hard fork never happening.
That's not exactly the same as "miners switching back to non gigablocks after 95% of their peers already have accepted gigablocks", "because reasons".
How about a miner, or a group of miners, broadcast v4 blocks, or even go as far as actually playing along with the fork, for the sole purpose of artificially inflating the exchange rate of gavincoin?
For an actor, or a group, with a reasonable chunk of hashpower, that would be a pretty efficient way to manipulate the cross-chain market and make a killing in the process.