DaveReidUK
I'm starting from the premise that the EASA directive probably is a compromise between an absence of explicit legal authority on one hand, but a strong intention to stretch what authority that does exist perhaps further than it has been applied previously. (This process - stretching existing legal authority to apply to a situation not previously encountered and not expressly covered by what's on the books - happens pretty commonly in U.S. legal processes, subject to due diligence beforehand and good faith, of course (see, e.g., Fed. Rule of Civil Procedure 11)).
If by "sanctions" we are referring to the type of penalties, barriers to doing business, and the like which are imposed by (say) the U.S. against (say) Iran, I don't imagine the EASA or EC has authority to do that.
However, a lot could depend on what happens in ICAO - specifically the investigation which the Council delegated to the Secretariat, having invoked Article 55(e) of the Chicago Convention of 1944. (By the way, are you aware of any prior instance of Art. 55(e) having been invoked by the Council?) If the investigation produces a set of facts which is broadly accepted as pretty conclusive or definite by a large majority of global civil aviation officialdom (CAAs, pilot organizations, Eurocontrol, safety-focused groups, and certainly the diplomatic corps of Member States of ICAO with seats on the Council, and Member States more generally within ICAO), that leads to one sort of next step (in my view). Even though not in the category of a conventionally defined sanction, a clear set of facts emerging from the investigation by the Secretariat would likely cause Belarus to become a kind of world civil aviation pariah. What practical effects this would have, may be unclear. But restricting overflights and barring entry to airspace of Member States seem accessible as a consequences, if not "sanctions" in the usual meaning.
Commonly observed in situations where rules have comparatively minor importance, or actually minor importance, is the observation that "rules are made to be broken." Is this not a situation though, where whatever the formal legal structure by and through which EASA exists and operates, those legal structure rules are made to be stretched in this incident? Stated differently, are there any pilot groups, or individuals with bona fide pilot experience and credentials, who would let this incident fade away, with just rhetoric and, ultimately a shrug?