So, two slight issues here.
If someone's kers fails, they're ****** because they can't go into the pits.. This seems to encourage drivers to drive for longer with failed kers in a hope it fixes itself, when in fact it could be causing more issues.
Second, if a driver messes up and stalls in some kind of spin, they can just restart?
kd
Yes, but in the latter situation you could also be preventing safety cars which almost always ruin races.
What happens if your engine stops working, your race is over, what happens if 4 tyres go pop, race over, what happens if your rear wing falls off, race over, what will happen if Ker's stops working, race is over.
Ultimately, Kers will need the reliability of current engines, but they should have that anyway.
With much more kers usage in the lap anyway, if your kers dies and you were allowed to come in the pits, who cares, your race is over. With current kers usage you're talking about 3-4tenths a lap, with far more kers usage we'll be looking at maybe 1 second + a lap. Kers vs no kers, and drs, there won't be a whole lot of defending when you don't have kers. so I can't see kers failing and people being competitive anyway.
Plenty of teams have a essentially completely reliable kers, only a couple teams constantly have kers failures, when the cars rely on Ker's more they'll devote a larger part of the budget towards it and the kers systems themselves will be several years more developed than when first introduced.