You'll probably want to get into the insider program to benefit from the latest bug fixes and new features, as Office-JS is under very active development, and user feedback is absolutely welcome and taken into account. The Microsoft Office Extensibility team is actively monitoring the office-js tag on SO, Michael being the top answerer in that tag. If your company isn't prepared to have all VBA code ported, then depending on how business-critical the VBA code is you'll want to keep a desktop install for the workstations that need to run VBA code. If your company is moving to Office 365 cloud, then your VBA code needs to be ported/rewritten in TypeScript, using office-js, from scratch: that should have been a cost that was factored into the decision to go all-web. Microsoft knows there are millions of business-critical macro-enabled worksheets out there running VBA code, and as far as I know VBA will definitely keep being supported on Windows. VBA will be supported on Windows desktop for the foreseeable future, but making it work on all the platforms Office 365 runs on is simply unrealistic, and isn't going to happen. That Microsoft managed to get it to run on Mac is rather impressive already, and I'm not even mentioning the fiendishly complex work of making a workable Mac-VBA editor.

VBA is a COM technology that has a lot of dependencies on Windows-specific things.

We've been told that we're more definetely moving to the Online platform of Office 365, and as you already know, Excel online does not supports macros -or any VBA really

Microsoft 365 vs office 2016 excel