Re-lacing in the old grooves is best practice, but not doing so doesn't make all that much difference. Go ahead and re-lace doing your best to follow the old pattern where you can, especially on the right flange where tension is higher.
Yes, it might be weaker and crack, (the operative word here is might), but than again it probably won't. It's a wheel and the odds favor it dying from an unfortunate meeting with a rain filled pothole before the hub cracks. You could end up building your 4th or 5th rim onto it before the hub finally quits on you.
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