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I vaguely remember this being discussed in a semiconductor course at uni (back in 1996 or so) - it was already an issue at the time in the smallest processes, and IIRC the prevailing approach then was to make sure that current flows both ways in the specific connections that were prone to electromigration - thus replenishing the supply.

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It was a major issue with aluminum interconnects. It was primarily addressed by switching to a different metal that exhibits less electromigration, namely copper. But you have to be careful putting copper in a silicon fab, because if it gets into the silicon channel, it kills device performance (copper doping induces a deep trap in silicon).

If the erosion is a statistical process then I assume that having the current flow both ways just slows down the erosion by some factor. I assume you could estimated it using some variant of the random walk statistical model.

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