Campbell Sloop
The bulkheads are there to stiffen the hull. Everything that touches the hull, and is not movable, should be 'glassed to the hull. When my H25 got moved recently, the yard guys put one of the hydraulic-lift pads on the side of the hull, at the V-berth. I rolled my eyes and waited to find the shelf and all my nifty new cabinetry had shattered and popped off. None of it had. It was all 'glassed to the hull, adding a degree of stiffness that kept the boat structurally sound (even the shelf along the V-berth; that's why it's there. Sure not for convenience!). This is vital to stressed-skin structures like our fiberglass boats; and I don't recommend circumventing it in any way.
When the Hunter 25 was new my dad conceived of a 'racing model' (he was always coming up with 'racing models') in which the whole inside was wide-open: compression post in the middle and just a bunklike shelf all the way around the hull at about the waterline, which we would then cover in carpet (it was 1974. I recommended playing Jeff Beck tapes when we exhibited it at the boat show). The problem with this idea, which is very cool to look at, is that structurally it's a nightmare. Some old-time Hunter aficionados here may recall the original H54 racing cutter of Warren Luhrs appearing at Annapolis in 1977. The boat had an internal 'roll cage' connecting all the stress points. 'What is the pipe for?' people asked.
My dad said, 'To hold the boat together.'
'Then what is the hull for?'
'To keep the water out.'
If you're doing without the structural integrity of bulkheads-- any bulkheads-- you will have to determine where else the stress loads can be transferred. On the Cherubini 44 we did without the annoying little cribbing bulkheads to support chainplates and created a massively-strong fiberglass web system transferring much of that load from the flange to the hull. This allowed us to use plain SS U-bolts for shroud attachments, a design I still recommend (being as I sort of thought of it).
The main bulkhead in your H27 is there to support the compression post and to tie together the sides of the hull-- both in compression (hull crushing inwards) and in tensile (hull spreading outwards). Any other bulkhead in the boat is more expendable than this one. Even though you have a large doorway cut in it, believe me that the little bit of bulkhead to port is still doing lots. The ones at the forward end of the head compartment do just as much. Yes; they do not seem to be fastened to the deck, having just teak facia boards up there. But they do maintain the vital shape of the boat, once hull and deck are fastened at the flange. Like a cylinder, if you hold any part of it from moving, the rest cannot move either.
You might look into some of the newer 'daysailers' out there, such as the Hinckley or the Morris, to see the arched openings they use at this crucial area. These elegant curves and ovals are meant to carry loads, not for aesthetics (curves being stronger than corners). Consider doing something like this, with good plywood, adequately 'glassed to the hull and deck, stiffened with some good-looking molding of teak or other wood along the edges, before you just eliminate what was meant to be there, for very good reasons, in the first place.
BTW it's not difficult to mend the rot, even with the bulkheads in place. I have done this many times, including in my own boat. Where there's plywood in the bilge, on Diana it's pretty much solid epoxy and 'glass now.