Well this is how i interpreted it: Sherlock was within his mind palace and hence you see them go back in time (its all happening in his head) and the bride is a metaphor for moriarty, as in how did he survive after he blew his brain out? Firstly you see that the death of the bride was staged but then you see that the "invisible army" was part of the death of the man because he "was a terrible person" and it was just many theatrical tricks that were played in order for it to seem like a ghost. Perhaps this meant that moriarty has people helping him and he isn't alone. Sherlock was a drug user thats why he kept slipping in deeper into his mind (think inception) and he concluded how moriarty faked his death, same principles.
Btw, Moriarty is definitely dead but people are using his name and image to create a scary legacy, like with multiple brides.
Fortunately i only recently learnt of sherlock so watched all 10 episodes in a couple days but for those of you who started from 2010 how do you survive waiting literally 2 years per season?