All the other times the park has built a big thrill coaster, the old one has been removed. Except Balder but he's wooden without any loops.
I don't think it won't happen this time, at least for a while. Since they now have more space than they know what to do with it, so removing rides for new rides due to space constraints won't happen. It may be removed due to that it won't have that much riders with Helix opened, I mean who in their sane mind would prefer Kanonen to Helix?
^This!
And if you think about it, Kanonen and Helix doesn't really have that much more in common other than that they're both launched coasters. They have different elements, are in different corners of the park and the launches will be quite different, rolling vs. stationary start.
All in all I'm very excited about Helix!