It seems that you have pretty much made the decision what status you would like to retain. The only issue is if you'll have the time/resources to do this.

Have you thought about having a few private/family weekend trips before the end of the year? If you have the time and like to do those that's probably the easiest way to add the few stays you need to renew diamond for the next year. If not, you can always do a few mattress runs, even w/o actually staying in the rooms you pay for. There are several options in and around Boston and some of the SSs or HPs can be had at a decent price. I would certainly do that to renew, especially if those stays come with FFNs as an added bonus (nothing confirmed yet). Both of those options mean money out of your own pocket but I think they are worth it if the diamond benefits mean something to you during your regular travel.

Other than actually paying for the rooms I don't know of any other way to guarantee the requalification.

One final note, IME it is always better to have at least one top status than to have a bunch of mid-tier ones. Hence, if there is no way for you to retain Hyatt diamond, by all means focus on Hilton and renew your status with them.