What can I do about a severed grounding wire?
Here is what the National Electrical Code says:

250.64 Grounding Electrode Conductor Installation. Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F).
(C) Continuous. Except as provided in 250.30(A)(5) and (A)(6), 250.30(B)(1), and 250.68(C), grounding electrode conductor(s) shall be installed in one continuous length without a splice or joint. If necessary, splices or connections shall be made as permitted in (1) through (4):
(1) Splicing of the wire-type grounding electrode conductor shall be permitted only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process.

So, the compression connector you have used there is not a listed irreversible compression connector. If it was it would be perfectly legal according to the NEC.
So, the electrician you talked to was not well informed. The Code allows the grounding electrode conductor splicing if it is done correctly.
Good luck!