I don't think EU had a strategy beyond offering UK a deal as close to the original membership as possible and hoping they would come around to understanding it's the only workable solution and the only one on offer.

EU may have suspected Mr. Johnson to negotiate in bad faith, or come up with every possible kind of shenanigans, but there's not much a consensus based organization of 27 members can do against a charlatan who insists on playing chess on a backgammon board while making up rules on the fly.

Pretty much the only thing Commission can do at the moment is to try to salvage the Good Friday Agreement. Sticking to legal issues and releasing the legions of lawyers is their only tool for now.

Maybe, if the 27 came up with short and long term strategies they could agree upon, and nominated a Commissar of Brexit to implement it in close co-operation with Ireland and Netherlands the EU response could be more pro-active and on a wider spectrum.

Maybe even a parliament with some simile of power in actual running of the EU could have an effect here, too.

My guess is that the EU will allow reality to intrude on the UK's intransigance.
If the UK crashes out with no deal, then it immediately imperils the GFA. No US Cogress controlled by the Democrats is gonna look kindly upon that situation.
And that puts the UK in a hard place every which way. No deal with the EU, no deal with the US and a deteriorating relationship with China.
There aren't really too many other places to go that replace all that trade. Which means that everything is going to start getting expensive on January 1st. JIT delivery schedules are going to crash. Hard. Bringing perishables into the UK is going to be difficult moving towards impossible.
Sterling is going to tank as both the City trade and import/export businesses collapse.
All of which is going to drive up costs in a sub-Weimar way.
I imagine that, unless boris has a cunning plan, he (or his successor, will crawl to Brussels on their bellies sometime in May.
By june there will be nobody left in the country who will admit to having supported brexit, but will be detectable for their red-faced apoplexy that the EU won't immediately have us back

keep to the Fen Causeway

Part of me feels the EU is responding so mildly because they just can't bring themselves to take Boris and his threats very seriously. Part of me feels the EU doesn't quite appreciate how much the EU is undermining the EU's whole raison d'etre and system of legitimacy. This still has the potential to go pear shaped in a big way unless clear and decisive action is taken.

As I explained elsewhere, the EU cannot do anything other than "going by the book"; and that means starting infringement proceedings at the CJEU and also continuing the negotiations with the UK - certainly not giving B.Johnson an excuse for putting all the blame of a no-deal on the EU breaking the negotiations before the end of the year.

As Barnier puts it:

🇪🇺🇬🇧 We will continue to maintain a calm and respectful attitude & we will remain united and determined until the end of these negotiations.

My statement following this week's round of negotiations: https://t.co/gUhAP9Zu4g

— Michel Barnier (@MichelBarnier) October 2, 2020

This said, the lack of audible noise from the EU officials and member countries does not mean they are not preparing for a no-deal come January 1. I even suspect that many EU countries preparedness plans are more advanced than the UK's "administration". Showing any hint of WTO or punitive tarifs on UK exports next year will only help the Brexiters as casting the EU even further into the villain's role. Even though everybody should be well aware that's exactly what will happen in three month's time.