This implies he does not support opposition in any way. This is not true. He does support opposition rallies—when they are held to support his cause, true, but such is political climate in Russia that publically supporting those who vocally oppose the state policy is a domain for very few and quite brave.
When Libertarian Party of Russia was organizing a rally in 2017 to protest Telegram ban, Durov contacted the Party himself. (I'm a member of LP RU.)
I don't count on Telegram security but Durov's public image and actions are certainly noticeable and appreciated by opposition.
It implied just that I don't know for sure and it does not change a lot. Even Khodorkovsky is not considered a threat worthy of eliminating - he much better serves the cause being a propaganda target. Durov has even more to offer to Russian gov't (digital technology is the new arms race) so he has even lesser chance of bodily harm.
There's absolutely no point in making any physical moves against Durov even if he was openly anti-Putin and supported opposition in any way. It's never done like that. He's already forced out of the country and is not considered a direct threat. He or his remaining actives may be considered a future asset, on the other hand.