Here's Safeguard's reply to my email yesterday (basically their policy continues to cover the EU whatever but you will need a free Green Card if no deal):
Good Afternoon
I can confirm that our policies here at Safeguard do provide comprehensive insurance cover throughout our territorial limits: Great Britain, Northern Ireland, The Channel Islands, The Isle of Man, Andorra, Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Gibraltar, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Netherlands, Norway, Poland, Portugal, Republic of Ireland, Romania, San Marino, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland and the Vatican City.
This is not due to change regardless of whether or not a deal is arranged as part of the United Kingdom leaving the European Union.
Should there be no deal arranged, and a green card is required for local authorities we can issue this for you within 30 days of the start of the trip you would require this for. We would need to discuss this with you over the phone to go through full data protection and request the relevant documentation from your insurer.
Currently there is no cost involved with issuing a Green Card in these circumstances.
Kind Regards