So it's probably no exaggeration to suggest that his departure across the water would have been, in the words of his agent, John Baker, "a disaster for Irish rugby". Some would compare it to the departure of a player like Brian O'Driscoll. All credit then to the IRFU for ensuring that he stayed in Ireland.
And it would be reasonable to surmise that he didn't come cheap. Asked about the financial package required to keep Williams in Ireland, Phillip Browne (IRFU Chief Executive) not surprisingly declined to give details. Williams himself said it was never about money. And again it can be assumed that the basic he agreed with the Union is somewhat short of what Saracens was offering. Whatever the bottom line, the Union can afford it.
However, the IRFU have now created a precedent. They have done so in the best interests of Leinster and Irish rugby. They have done so at the behest of heavy hitters in Leinster who believe that with Williams in charge, Leinster can lift the European Cup sooner rather than later. Few would disagree.
However, it poses this question for the same heavy hitters. Had the same tide of technical and personal support come flooding his predecessors' way, would we still be waiting for Leinster to hit the high-water mark?
A part of the deal Williams signed up to, envisages a new stadium at Donnybrook (plans already well advanced) with state of the art gym facilities, a new training pitch, a staff structure and whatever else Williams (he) believes it will take to make Leinster in his words, "a team that can be competitive on a regular basis in Europe".
Meanwhile, down south, Munster is in the process of replacing the talismanic Declan Kidney and Niall O'Donovan. The logic surely, is irrefutable: if the IRFU are prepared to burrow deep into the coffers to help Leinster achieve European glory, then they must do the same for Munster.
After all Munster have already tilled the field that Leinster yet hope to plough. Their European exploits are the stuff of legend. They're a sponsors' dream with their Corinthian spirit and passionate, inclusive support. So now, after the Holy Thursday annoubcement, Munster presumably can look beyond the confines of what, until the Williams era, was the standard Director of rugby pay scale.
And up north, Alan Solomons, coach of the 1999 European Champions, Ulster, after signalling a return to form this past season, can presumably be confident that he will get whatever additional help he needs, financial or structurial, to return his side to former glory.
Connacht's Steph Nel exploits to date, with even fewer resources, have been highly laudable. No doubt he too believes that his province is as worthy of the same investment as Leinster. Galway is a vibrant city with a population profile cherry-ripe for the type of marketing that would swell the Connacht coffers.
Whether rugby, in truth, has an all-Ireland dimension is about to be put to the test.