Could it get to the point where mining actual Cryptocurrencies comes to an end?
No, there will be no end for mining. Remember on how transactions are being processed with bitcoin? It needs to be confirmed with miners so I don't think that there will be an end to the miners or there will be time that we don't need miners anymore.
We need to use as less energy as possible while making our transactions.
Energy is costly and energy hungry process of confirming a transaction by mining is getting more industrialized that also undermines the decentralized nature of crypto currencies.
This is the disadvantage of mining, not unless there will be a change for those coins that needs confirmation through mining.