They can do that , With player as a host . And most important , if they do that , they need to add a block player button , because there would be a rush of cheaters in such casse , so u would need to block such ppl if encountered .But , i somehow doubt that . Because they would not make any cash of doing it .And most companies rather burn and burry the ashes instead of release it for free .

Then just interesting card packs and stories as dlc?
So no, there isn't not any money to be gotten.

Because it would cost a lot of dev time (read: cash) and would gain nothing out of it
We know from the actual time it was being developed and then stopped that they don't think developing for it is worth it

so the cash they are explected to make is lower then it will cost?

They are so wrong, because even keeping only registration (people subscribe to a service with an email) and then allowing offline play would give them tremendous value (thanks to the users and emails they will get, allowing future releases of any game to be a success).

The whole shutdown process was a mistake.
This was my 12-year son most appreciated game of all time.