To be honest, $26 billion worth of Bitcoin of Bitcoin is not something to joke about, that's a fortune and if a company such as Microstrategy would keep adding too their reserve instead of selling it means they've pictured the future and saw that you can't write it without including Bitcoin, it's the future and there's better times ahead. Also, never forget that a win for Bitcoin is win for every Bitcoin holders, Cheers.
MicroStrategy has really built great wealth in bitcoin but i still have the feelings that they have a target and when that target is met, they will consider selling some of their bitcoins. Perhaps, as they are making news while buying a lot of bitcoins, when they sell, it will also affect the price of bitcoin.
On the other hand, it's kind of scary to me what will become of bitcoin (aside from the increase in value) when more institutions try to bag bitcoin as much as they can and the government joins the train too using bitcoin as a reserve. The kind of unstable price and how easily those entities can manipulate price and cause panic to the market is what I'm afraid of.
Am also afraid as you are because so many bitcoins will now be left in the hands of these institutional investors thereby leaving individuals with few or low bitcoins in their custody which means that we can just wake up to an unfavorable news especially when they start to consistently manipulate the market.
Regardless of the fact that you're speculating, I see some point in what you're saying, yes they'll definitely sale case they can't hold forever but it's going to be a very long ride before they'll think of selling, I see Micro strategy as a company that's pictured what the future would look like with bitcoin and decided to pump lots of cash flow into it against the future, so i think they'll definitely sale but not anytime soon.
It could be it could be in about lots of Circles let's say 3 to 4 more circles or thereabouts and I'm pretty sure they'll be on a huge profit side when they sale, moreover they won't be sale everything but some portions of their portfolio just to continue being one to the top holders in future, everyone who's understand Bitcoin well would know that's the rightful thing to do.