Drive Shaft / Gear Box Issues - Honda Civic 5 Door Hatch 200

[TheGuyWithThatUsername]

**** Disclaimer this is LONG, and probably boring. Skip to last paragraphs for key Questions ****

Let's start by pre-facing this with "basically I don't really know what I'm doing, but I'm learning......."

Car failed MOT (UK) for split CV boots. I had some brand-new drive shafts in the garage (can't recall why), so I figured I would just swap the shafts over. I'm working on the ground as it were with the car upon stands. I'm ok with brakes etc so stripped it all down, popped off hub nuts etc and (eventually) popped the old shafts out.........

This is where the fun begins!

Didn't realise aligning and fully locking a new driveshaft in could be such a pain, probably a doddle when you've done it a 100+ plus times but everybody’s start somewhere right.

Managed to get both shafts in securely (so I thought) and felt very impressed with myself. Even took it for a brief drive up and down the road and nothing exploded or fell off. Parked up, came back out with the intention of going back to get the MOT ret-test done. Reversed off the driveway, went hard lock, heard a clunk / bang and suddenly no power or gears.................

Eventually figured out one of the shafts can't have been in right and it must have popped out.

Had enough for the day by then, so tidied up and walked away to come at it fresh another day.

Came back to it a few days later (with a helper this time), stripped everything down, popped both shafts back-in, re-assembled (checking for engagement every step of the way by rotating one shaft and checking the other with box in Neutral). Seemed sorted.

Again, drove down the drive, relatively sharp turn and lost all power. FFS!!

Ok, clearly one of the shafts still isn't aligned and locked in correctly - no problem, I know which one it is this time (NS passenger) as its pissing transmission fluid. Seems the slip-ring or whatever you call it just isn’t fully engaging and locking the shaft in place.

Called a mechanic mate, he suggested opening the split ring slightly and trying again, so I did so. Felt like it clicked in, but when I tried to hand rotate to check engagement, no movement on opposite shaft.
Starting to get puzzled and pi**ed off. Thought right, let’s try the original shaft and see if that engages. That wouldn't go in at all. Re-checked new shaft, only to find there's no longer a split ring on it...........

Bugger - said split ring must still be in gearbox splined mounting sleeve. Now, bear in mind I'm lying on my back and can’t see the gearbox splines. It's also now dark and I'm working by lantern & headtorch..........

The driveshaft isn't in place, so I feel around with my finger in the gearbox and sure enough I seem to be able to feel a split ring loose in the casing. Tried to get a grip on it and pull it out, not sure I've succeeded. However, I can’t feel the ring there anymore so it must have gone somewhere right. I must assume worst case scenario and it's gone further into gearbox. Have tried fishing out with magnets (assuming it's even in there), but the magnets seem to just stick to everything and even when I get them beyond the splined sleeve and below the diagonal / vertical shaft in the middle of gearbox they don't seem to be fishing anything out.

TLDR - I may have lost a split ring off a driveshaft INTO the rest of the automatic gearbox.

Q1 - If I have, any tips on getting it out?

Q2 - If I can’t get it out and attempt to drive what are the best and worst case scenarios.

Walking away for a day or so and then coming back fresh (again) to check under car and everywhere else for a loose split ring. See what happens from there. Wish me luck all!!