I mean imagine, you've Bitcoins but there isn't much cash available in the market to buy your BTC, or simply put people can't afford it? Will bitcoin be of any value then?
Yes, still there will be value. Because many peoples can't afford to buy 1 Bitcoin currently but they have been buying in satoshi. Then the same thing will happen if BTC surpassed fiat value. I don't think the price will go out of affording, but if happen then there is be an upgrade chain with more decimal. So, then everyone would buy that. Also don't think there will not any Bitcoin competitors in the future. Who knows if bitcoin exist or upgrade in new technology after a hundred year?