I think a good way to circumvent this problem
What problem? I haven't seen anything about a problem yet.
is to not to limit the amount of BTC to 21M. Instead it should have a deterministic inflation rate of let's say 1%.
Inetersting idea. You should create your own cryptocurrency that uses that design and see how many people you can get to adopt it. If it is a better design, then it will be more popular and will replace bitcoin. You won't be able to change the design of bitcoin though. It would require a consensus of all users to implement your idea. Do you really think you can convince every paranoid, tinfoil-hat wearing, consipracy theory believer out there to accept a change that will lead to inflation?
First the concept of mining as it works today could go on for ever.
The concept as designed today can already go on "forever" (well, nothing lasts forever, but I get what you mean).
Secondly, deflationary forces such as loss of BTC, could be compensated for.
They are already compensated for. When bitcoins are lost, everyone elses bitcoins become more valuable. If they become so valuable that it doesn't make sense to price things in bitcoins, we simply price them in millibitcoins, or microbitcoins, or nanobitcoins. No problems there.
I general inflation as it is today is not a good thing cuz it takes monex from the savers to the speculaters, but if the inflation rate is small and deterministic it would be a good compromise.
I'm not sure what you mean by "deterministic", but why would inflation be good?