For what it's worth, I think practically speaking option 2 covers the most ground. You followed the document (and law) by allowing diversifications during the plan year based on the most recent valuation, but have built in a mechanism to ensure the participants are not harmed in the end.
The deal is not close enough to know the final transaction value. If there's not a binding LOI, one more month will not produce a final deal value either. At this point in the year, you'll be lucky to close by year-end, which means you'll need to decide if you want to skip payouts altogether for the entire 2024 plan year. As I'm sure you've seen, deals fall apart well past the signed LOI stage, so in my mind trying to approximate the deal value a month from now and pay it to diversifying participants is a non-starter.
An interim valuation would not help, in my view, unless it also accounted for the pending sale, likelihood of closing, etc.
Option 1 presumably would require an explanation to participants, as ESOP Guy notes. I'm not sure what added benefit would be achieved by not diversifying at all. Plus, it seems to me that it would pretty clearly violate the plan document and statutory diversification requirements. In almost all cases with a strategic buyer, the deal value will be higher than the most recent valuation (if it's not, that's a separate fiduciary concern), so in reality you're likely only to be increasing prior payments.