After the halving, the price will be higher. Even if people sell the bitcoin, the price will not be below $500.
I am quite sure that $500 will not hold for long once the price start to tank heavily after the halving. It will go up again but it will cost some time. Building up the price cost many months while all that effort can be undone in a matter of a day, or even some hours.
If the price does not reach $700 before the halving, the price will not drop below $500. There will not be dump if there is no pump.
Pump and dump is bad for the bitcoin. I still remember the big pump in late 2013 and the two years of dump.
Small pump and dump is good for the bitcoin or other altcoin. It can attract media attention and make more people know the coin.