Cashscript forces bigints in appropriate places now I believe, at least on the cashtokens upgrade version. But generally speaking you will have to take care of those safety boundaries yourself. The risk is that your app or library makes temporarily unredeemable (e.g. until app/library upgrade) or permanently unredeemable (e.g. putting money in a contract that will end up calculating negative outputs or less than dust outputs etc) contracts.
It has been less of an issue until now because all the satoshis in the chain fit in 51 bits. But start to do multiplication, division, etc. or work with large cashtoken amounts and you can easily break it.