The MR42E has no internal antennas whatsoever, so in effect it will not work without external antennas. I don’t know if Meraki took the effort to either block the radios from coming online without an antenna attached or otherwise safeguarding the unit itself from physical damage, but even if that’s the case, you effectively will have no wireless coverage.
In my line of work I have tested client devices with no antennas attached and they have maybe 6 inches of wifi reception at extremely low data rates, enough to get an IP address... but it’s effectively useless.