Polkadot and Uniswap are coins with a transaction value of billions of dollars per day and this indicates a lot of investors are investing and trading. With such a daily transaction value, I think both tokens will last as long as they are able to maintain their project performance
They need to continuously innovate to adapt what is the current trend in the market. Because if they will not add or improve their features, they will be left behind by new platforms with better technology. Also, as the fees is the major consideration of most traders, they always need to be competitive in fees or else, these users will easily jump off to other network like what is happening now, a lot are moving to BSC network.