That depends on how much time it takes to develop and maintain the interface to the external dependency. Also, there's little risk if it's a well supported standard open source library with many users, but if it's a proprietary library or a tiny project with a small user base, what can be done to mitigate the risk of it going in a direction that is not compatible with your own use case? In the end, you may end up having to work with and maintain your own fork of the code anyway, and I doubt that it would be easier to do so than something you wrote that was tailored to your own needs.