Consequently, you can't actually expect to capture 100% of these analytics events nor even expect the percentage captured to stay the same over time since the filter lists are very regularly updated and users enable/disable different ad blockers over time.
More broadly speaking, once you have sent a webpage to the user, you should not expect anything from the user's browser. They may or may not allow whatever arbitrary JS you have on the page. They may even intentionally give you bad data (e.g. hijack the payload to give you intentionally malformed data).
edit: even more broadly speaking, there's additional reasons why you can't expect to receive these kinds of callbacks: consider what happens if a user loses connectivity between loading the page and them navigating away (e.g. their phone loses service because they went into an elevator before navigating away)