Will someone have access to your wallet without your device but the person manage to see your private keys and copy them without your knowledge. Will the person be able to withdraw your money or change password and block you from having access to your wallet?
Make efforts to store seeds and or private keys as well as possible and as safely as possible, even be willing to spend money, including avoiding internet connections and keeping investment activities secret from unknown people so as to ensure that all assets are intact in all amounts.
I would say they can perform any action when the private key and or seed is known by someone else.
Use it well and take good care of it before someone else discovers it.
Create security in layers, create strong passwords and avoid sloppiness.
When you don't care, everything is in vain and you will regret it when it happens.