I think more than anything, the people who care about Sanders' endorsement aren't very likely to go vote in things that Sanders isn't in. Maybe not any less likely than other voters, but the Sanders camp has relied on invigorating a lot of first time voters and the like but if they don't turn up then the endorsement is not very good.

Moreover I think Clinton's endorsement is very strong, it will reach a lot of people since his presidency is remembered fairly well. It's certainly way better than Bernie's, add on Reid's and Bernie's is kind of meaningless.

I don't think it will weaken his leverage, that will almost entirely depend on how much goodwill he can scrape out of the barrel. He was a surprisingly good candidate at mobilising anti-establishment types and he was against a woman who is actively disliked by many voters. He still lost fairly convincingly and then he threw a tantrum.

It was a mistake in terms of keeping goodwill, however he made a gamble and thought he could get enough delegates to warrant making demands at the convention in excess of what he had + the goodwill he had. It looks like he gambled wrong.

There isn't going to be a revolution, however he can try his hardest to campaign for like minded candidates in states favourable to him like New Hampshire. If he wants to promote his type of ideology, he needs to avoid making it seem as though "it's all over" after he loses and just diligently work on promoting certain candidates. I don't know if he will do that though, and I have no idea if he'll be at all successful aside from maybe one or two major victories and a few smaller ones like state senators