I’m considering a similar course of action, selling off a bunch of modular to improve my recording setup and only keeping the essentials.
As Andrew and Alanza point out, feedback is the main thing that digital can’t do, by it’s nature. There’s also the non-linearities that give analog circuitry their warmth, but emulations are catching up to that.
But putting those aside, the difference I notice is often in the design approach: eurorack is full of modules with unique functionalities that could exist in software (they’re often digital to begin with) but don’t, and the flexibility of plugging anything into anything isn’t at the same level. Software is slowly catching up there as well, but that’s the main thing I would miss.
So for a small euro system, I would focus either on a complete synth voice, something that could be used to perform with standalone, or a signal processing case with a matrix mixer and a bunch of oddball filters, distortions and effects.