But everyone experienced in such a "migration" would challenge your flawed impression that there would be cost saving. SAS is in fact used in many serious companies (I know it's used at the fraud department of Bouygues Telecom, for instance) so you're not gonna dead-end yourself all that much, you can do the python+r stuff on your own probably, as long as the reports are there, and call them from SAS if you cannot stand it.

Meanwhile, nothing has to move, nothing has to change, and your non-critical division will continue to cost exactly as budgeted instead of going through unknown waters just because maybe switching to something new might be ... cheap eventually ?

Plus this has nothing to do with Microsoft really, as most cost is in Windows and its integration. It's hard to replace the global policies of Windows by an alternative.