This question came up before and IIRC .NET FW is only required for the installation package of SQL Server, not for the actual product itself.
That said, if you have any SQLCLR objects or types (built-in like Geography/Geometry, or user-defined) in any of your databases then I believe .NET FW will need to be there for those to function.
As mentioned, make sure you test in a non-prod environment ;-)
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