Companies are businesses must obey laws and regulations in their country and even regional or global regulations. Therefore, companies must feel safely enough to own bitcoins for their companies first as it is allowed legally in that nation. Next, they must see demand of their employees so that they can consider a salary payment policy change from fiat (cash), bank transfer to Bitcoin.
Things must come this way, gradually and legally, for having sustainable and acceptable policy in any company. If employees don't have demand of having bitcoins, it's hard for any company to force their employees to receive it.
Actually, suppose the purpose is only to pay the salaries of their employees and not making investments for the company itself. In that case, a company doesn't need to buy and own Bitcoin at all times, but they can always just buy Bitcoin worth the amount they use to pay to their employees, and then pay them their salaries based on the value of Bitcoin at that time, or by the time they bought the Bitcoins. However, if the company wants to invest in Bitcoin itself, just like MicroStrategy, they can always keep buying and storing every month with the revenue they are making, and then pay their employees with that.
Also, it's obvious that a company can't force its employees to accept a certain asset as their salary. Still, it should be paid in the standard currency of a country, unless the employees demand that they get paid in a certain currency that is easily accessibly by the company. Then the company may decide if they want to entertain the request or not. If the company thinks it's not easy for them to do so, they can always reject the requests and pay them in fiat instead.