It only can't unilaterally if you expect a major increase in the amount of stake voting for witnesses. That includes stake held by dormant and even dead stakeholders, lost keys, etc. I don't expect this.

Not to try would demonstrate a high degree of negligence.

Even if you assume that there is enough stake actively voting such that 37.5% isn't enough to literally exert unilateral control, it is still highly dominant. With the slightly simplified model that there are two distinct slates of witnesses and it takes >50% to vote in one slate, the 37.5% only requires 20% support from the rest of the stake to reach 50%. This could include app owners with stake who are bribed (which need not be directly nefarious, but could include offers of funding for marketing, development, etc.), people who are confused, people who are swayed by marketing/campaigning, etc. Getting 80% of any group to agree on anything is not easy, and certainly much much harder than peeling off 20%.

Now you're making assumptions. But thank you for detailing them.

But realistically you are not going to get all of the rest of the non-voting stake to participate, so even if you could possibly get enough to participate such that 37.5% is strictly below 50%, it would not be 20% that needs to peel off but maybe a few percent at best.

In the short term, nothing will change. According to Steemit, Inc employees, the Tron Foundation will continue to fund ongoing development at Steemit, Inc. The Steem blockchain is not going to get axed any time soon. It would take a lot of work to replicate the functionalities of the Steem blockchain in smart contracts on the Tron blockchain.

In the medium to long term, it seems that Justin Sun's plans are open. It is not unusual in the tech sector for companies to acquire other companies without knowing exactly what they're going to do with them. The Tron foundation has acquired Steemit because they have some kind of a rudimentary vision of what it might be useful for. Those plans will take shape as we go along in the next year or so. There are no clear cut plans to shut down the chain and set up shop on Tron any time soon.

When I listened to the Witness Forum yesterday, it seems that most witnesses are on board with the idea of having some sort of mitigations in place in case a hostile takeover would take place. I think those mitigations including, in my view, getting every stakeholder to use all of their witness votes, working with exchanges etc. are very important because they signal to the Tron foundation that his community values its independent existence despite being more than willing to build bridges and co-operate fruitfully with the Tron foundation.

Total mental capitulation at this stage is worst imaginable course of action.