There will be bunch more artifacts/prestiges/late-game-upgrades, so most likely some of them will have ways to generate mithril/souls. One of them for example would be a ritual that forges mithril into a dwarf simulacrum, or a dwarf into mithril haha.
Wow, you must have a beast of a phone, since not only do browsers run poorly, but my phone really struggles to get decent fps even early game. But yeah, the game isn't designed for mobile in any way, though I hope I will be able to properly support it after a successful steam launch.