For example of what could happen if it does you can see this thread for Tiziana.
If they do moves to a US market like this, you will need factor in that you may very well need to pay fees and tax for the stock to move.
How many shares you get would depend on where they list. Some may require require the shares to be worth over a certain amount, so some sort of consolidation may occur, eg. 2 → 1.
After a move, you will also have to factor in whether they will be supported by Freetrade’s US execution partner. The market cap for this stock at the moment is tiny, and I think Drivewealth will likely not add it to be traded as I think they may require a minimum market cap size. - It could be listed as ‘sell only’ status.
Alternatively the route could be the ADR like Argo Blockchain did, retaining the UK stock listing.
Eitherway, if some sort of US listing was going happen, I would be reading through details with a fine-tooth comb to determine what the best outcome for myself would be. Neither of the above outcomes have been particularly advantageous to smaller retail investor.