Here's a suggestion. You can only do split paths, but it's very tricky.
1. Add a duck'ing reverb block, with mix at 100%
2. Move the block to a parallel path.
3. Now on line 2, what's coming in is your guitar signal, what's coming out is ducking reverb only.
3. Add a sensible amount of delay after that on the same line, a few repeats, not 99%
Now as soon as you stop playing notes, the duck'ing reverb engages, and the signal goes to the delay.
Ducking reverb is sweet. It lets your entire note ring out, and when you stop playing, it creates this wall of sound. You need to play around with the pre-delay and feedback parameters.
Duck'ing reverb works great on the Helix, and if you put it in parallel path, you can add a bunch of effects after it, mix it however you want.
If you can't get the duck'ing effect working, if it's not automatically disengaging as you need, you can always assign things to the expression pedal and mix your delay out, or even bypass it.
Not really related, but I crated a preset that creates a synth pad, all using parallel paths. So you may find it useful how to organize things in all those parallel paths.