After a character reaches Doom 6 the GM can bring about their final scene at any time. I assume you would work it into the plot at a convenient moment. In the meantime, can the player keep calling on their Doom? For example, can they get six bonus dice, seven bonus dice, etc.?

Roger,

I would say no (and should have been clear in the text on this) cause their Doom is at hand and it can't go up in rank anymore.  As the GM I would try to introduce it as soon as possible, even at the end of the scene if possible and as a Player I would want my tragic final moment to come soon cause that gives me a chance to go out with a bang.

Keith