It's safe to say the amount of new miners joining because of the crypto bullrun is why were not seeing significant drops in hashrate. Most large miners already sold off and phased-out the 4GB cards. While new miners are buying older RX580 8GBs, 5700/5600XT's or Nvidia GPUs with 8GB ram or more. Lastly Zombie mode was invented by Miner-software Devs keeping whatever 4GB cards are on the network until they're unprofitable for that person. For me, I'm keeping my 4GB cards on until Feb a Full month later thanks to Zombie Mode.

So unlike everyone was expecting there will no 'massive' drop in hashrate.