Filling a hole
OK, so I first tried redoing the Tspline mesh body myself, but could not get the patch to work either, I guess the combination of the very elongated hole with almost sharp corners along with the 3D curvy geometry is just too much for the Patch tool. So then I tried using the Fill Hole in the Sculpt environment, but the results probably are not what you want, although now that I think about it, likely can then use Edit Form to move back into a kind of shape that looking for. So I ended up creating a patch via extruding the sketch I used to cut the 3D curve into the body, then did a Boundry Fill to make a solid body, and finally used the variable fillet option in the Fillet tool to make a decent looking end I guess (not sure exactly what you're going for though).
I've attached the .f3d file. Let me know if you have questions about anything, including the alternative method I really didn't try of using Sculpt fill hole then Edit form to get back into right shape.
Good luck!
Jesse
I've also decided to try using Sculpt to model the end, which works pretty good, although I'm not quite sure how to form the very sharp corners, except to keep adding lots of faces/vertex points. I'm curious if there is a better way though.
Ah, just need to use Crease tool and know which edge to choose!
I also had internal symmetry turned on so same is done to both sides of tube.
I created this by using Merge Edges to close the opening at the top, then Utilities > Repair Body and Auto repair to fix two problems at the corners (which were then added back after doing some Edit Form modeling, by using this crease tool).
Takes some getting used to, but Sculpt really is a powerful modeling system!
Jesse
Here is the tube with the whole end having a crease/sharp edge (using the Crease tool in Sculpt), if that's what your going after.
Note that the box mode (by Alt 1 or Alt 2 in windows) is very helpful to get at the control frame to move node points around for achieving desired curvatures.
Jesse
Yet another option is to thicken what you have, including in an outward direction, then with that new outer edge include it as 3D geometry in a new sketch, then extrude that in Patch workspace, and then you can successfully apply a patch to that extrusion in either Connected or Curvature mode (not tangent surprisingly). You can also fill this "heat seal" area of the tube solid using Boundary Fill.
Jesse