What you say is true. They can sell shares without selling a single Bitcoin, but what about the new buyers of the shares? They will become owners of Bitcoin. Do you guarantee that they will not sell Bitcoin? Then we will return to the first question: If they sell these huge amounts of Bitcoin, what will happen to the price?
I think you getting it wrong
They are buying the shares of Microstrategy not explicitly Bitcoin
The shares are been bought because of Microstrategy holdings of Bitcoin
This can be seen from the increase in their valuation of share since early last year.
Now moving on to OP question
1. Imo is their choice. Is their holdings they can choose to continue holding or selling, but we can't tell when that would occur.
2. If it's to take profit, there wouldn't be much impact. The Bitcoin would be sold in smaller units that it wouldn't affect their market
Don't forget their recent Soaring valuation is as a result of Holding Bitcoin
Many investors are interested.
If in case of liquidation, Then there would be a short term dip but the market would correct itself and the sold Bitcoin would be shared and reduce Centralization.
3. I don't really. If you swayed by their actions you would fall under market manipulation tactics that most usually employ.
I just hope they sell, the more they sell the better. That's because I hate centralization and any centralized entity owning a large number of coins, specially when they do it with other people's money.
Grayscale is a living proof of this defect.
If anything happens to the firm
Shareholders would start withdrawing and Microstrategy would have to sell their holdings to meet up with their investors demand.