yes, you will still be able to use those characters for as long as you register your game key on that trial account.

Also i remember the possibility to buy a game key online, which costs half of a real cd, so 10 USD. i'll look where you that was.

edit:
http://www.codemasters.co.uk/eshop/l...?name=archlord
here you can buy a digital key directly from codemasters. You can then register this key on your trial account for full, timeless acces.