What is the voltage drop across each open switch in series connection?
In case of ideal model, in principle you could have any combination of voltage, provided that the sum is E. However, if the devices are exaclty equal, for symmetry and "continuity" (i.e. limit R-->inf) reasons, the voltage on each device would be still E/2.

Instead, I have doubt on the real devices, as, for sure, they are polarized in slightly different conditions, hence their off-resistance might not be exactly equal (not no mention device-to-device parameter dispersion).