Abstract for version control and Zeplin for handoff. It works.
Our front-end library is essentially coded components which has worked really well for us. Our Sketch files simply get outdated far too regularly for us to invest too much in a library (though we have one). The nature of design mocks is that they are essentially useless beyond the initial release.
Right now my team is using InVision to share ideas and aesthetic choices, Sketch Cloud for version control of our design system, and Zeplin for handing specs to developers.
I'm not really happy with it, but I haven't found a better solution.
Are you on the enterprise? I feel like this whole experience will be improved when InVision v7 rolls out.