Assad don't want to invade the Rojava, and he has made this clear many times. But there are two pro-Assad enclaves inside the Rojava (Al Qamishli and Al Hasakah), where hundreds of thousands of non-Kurds live (mostly Sunni Arabs, Assyrians, Alawites, and Armenians). These people don't want to live under Kurdish rule.
They want to live under Assad family rule for ever? Why are only eastern Ukrainians and Crimeans allowed self determination? Why is the Ukrainian gov less legitimate that the Syrian one?