On 4GB video cards, you can mine other coins, where the DAG file has not yet exceeded 4 GB. Or mine Ethereum Classic and wait for the price to rise to $100.
It can be a joke to some but if Ethereum goes truly PoS then the first coin that the Ethereum hash rate will migrate to is the Ethereum Classic which no matter how low is now it is still profitable to mine with for example a rig of a minimum of 300-350 Mhsh.
Mining Ethereum Classic is my plan B if Ethereum goes for real into PoS which I doubt will happen this year as that would brutally crash the price to like 20-30 USD per Ethereum before some kind of recovery starts and in the long term no one will want to have anything to do with Ethereum then.I am liking that the difficulty for Ethereum Classic is going down from 350 T to less than 300 T now.