Last time round many lines ran without incident.
I’m sure there will be some impact, but with so many people now able to work from home or take alternative means (bikes being really a game-changer from this perspective) strikes really don’t have the impact they once did.
You have to remember that there are many people working for TfL who aren’t in the RMT. They will continue to work.
The reports state only 60% of the RMT membership voted to strike; I haven’t explored the numbers in detail, but I wouldn’t be surprised if that 60% was actually the typical “of those who responded” rather than the total membership.
As ever this is likely to result in a minority of RMT members, who form and even smaller proportion of TfL workers, withdrawing their labour.