It would. If more government R&D had gone its way, then as fast as it was. If not, maybe with some years of delay. As I mentioned to jandsm, the delayed technologies were eventually built into later versions of the train.

Any idea how decisions about how much to retrofit & how much to build new are done & what expertise is involved?

This train was all new, so no retrofit here. The new technologies used weren't entirely novel either - in fact most were developed by German firms. But to build any new train in Europe, epecially for conditions that didn't exist before (like - going faster), you have to design all parts to work together, and prove that they do in tests. This costs money (and so does building the new equipment, so to make that cheap is part of R&D) - so cost-cutters may decide to not use something, or use some old technology instead that is known well enough to be adapted more easily.

Now your question was about the decision process - that's usually some high boss sitting down with an R&D boss, looking through what costs how much, and the high boss making the decision in the end. Which is often silly, and some in the R&D department already see that. I don't know it closer than that.

was there any legislative action was taken as a consequence (either hasty or after the initial media frenzy dissipated) of this derailment?

None of the kind Jérôme mentioned that I know of. The trains were first taken off the rails, then allowed back with standard wheels (speak: a lousy ride quality; I travelled in one), while a jury investigation was left to run its course. Unfortunately, and as all too usual, there was no verdict coming down hard on the responsible higher-ups. Meanwhile, there have been programs to retrofit the trains with window-breaking points and on-board sensors, and to better equip maintenance centers, but AFAIK without 100% coverage so far. Same for track-related issues (e.g. switches, bridges).

_{*Lunatic*, n.
One whose delusions are out of fashion.}

Definitely!
As DoDo mentioned the alternative Maglev is very expensive so some sort of high speed train would definitely have been built.

Following up on a comment by Migeru was there any legislative action was taken as a consequence (either hasty or after the initial media frenzy dissipated) of this derailment?

As far as I know, no. The government pretty much stayed out of it.

What happened in the immediate aftermath was a frenzy of checks by the railway company.
June 4: Speed limit of 160 km/h for all ICE 1 trains
        and ultrasound checks of all wheels
June 6: All 59 ICE 1 trains recalled for ultrasound
        checks and not to be used until checked (even
        the 15 already checked since June 4)
June 13:Once again all ICE 1 trains recalled. This time
        because of the supervising Federal Railway
        Agency.
        They found similar problems in some urban rail
        trains using the same wheels.
June 15:The Federal railway Agency forbids the use of
        this kind of wheels. All have to be exchanged
        for standard wheels.

(According to the websites I googled the accident happened on June 3, not July 3?)

Additionally, checks all across Germany if there were similar switches before possible obstacles. Any new built tracks since then don´t have switches in potentially dangerous zones and new bridges - if possible - don´t have a "pillar" near the tracks.
Of course I don´t know how much retrofit was done.