I'm so sorry for your loss xx
Passing clots is normal for what's happened; your pregnancy has come to an end, hCG has therefore started to drop and your body is starting the process of expelling the failed pregnancy.
In terms of how much blood and tissue you've lost, the blood loss is concerning and is not normal. However, everyone's case is different and everyone is different with how they cope.
I'm just at the very end stages of an MMC myself. I lost mine at 5 weeks, but it wasn't caught until a scan at 7 weeks. It was an empty sac/blighted ovum. After two heavy bleeds, the sac ended up at the top of my cervix and then passed on Boxing Day last year. So yeah, Christmas 2023, alongside being scared out of my mind about retained products etc I can think of better ways to end a year, like, say not miscarrying and enjoying Christmas. Anyway....
I had 4 haemorrhages in total, all of them passing big clots. I didn't go to the hospital because I didn't need to. I managed it all at home. Granted being sat on the toilet isn't nice, but it's better than being somewhere where you have no access to a toilet while you're having a big bleed. You may feel differently for your specific circumstances and prefer to be in A&E.
The reason you get clots is because your lining is still highly vascular at this stage, so when your uterus begins the process of expelling the lining, the blood vessels that are supplying the lining rupture and as a result, it's like turning on a garden hose. The blood rushes out, coagulates and then once the clot gets too big, it passes out. Then another clot forms, gets too big and passes out etc this will continue until the bleeding naturally tapers off, and I assure you it will taper off.
All of this is why the go-to with missed miscarriages beyond about 7-8 weeks is to have a D&C. You don't have to worry about sudden, random haemorrhaging like that and you can draw a line under the loss and move on to try again as quickly as possible.
Generally, you are fine to let your body do its job, just so long as you are aware of the signs of uterine infection. If you suspect an infection, get yourself to A&E immediately. Also, keep an eye on your hCG levels and test once a week, you want the levels to go down. It can take several weeks for hCG to bottom out to nothing, but as long as the tests continue to get lighter, you'll be closer moving on and trying again.
Miscarriages, be they spontaneous or missed, are truly devastating and I will say again, I am so, so so sorry for your loss xx