If you had a default .bashrc file w/o your own tweaks you can recover the original one from the skel directory:
cp /etc/skel/.bashrc ~/
The skel directory has (or should have) the default settings for new users. When a user is created the contents of the skel dir are copied to the new user home
Added a description of how to check what could have been in the user's bashrc file that is not in a default bashrc file:
In case you had a tweaked .bashrc file and since env
will dump all the session settings (lot of stuff) which may proceed from several files (/etc/bashrc, /etc/profile, .profile,....). you need to get what was generated from your own bashrc that is different from the default bashrc, and discard all what is generated from other bash sourced files:
Based on the 'env' answer posted by silviud and as long as you still have the old terminal open you can save the env
output to a file. Then open a new shell and compare old env to new env hence showing what was generated from your .bashrc.
For example, in your old terminal dump the env to a file:
env > oldenv
In a new shell get what has changed now that .bashrc is the default one:
comm -3 <(env) oldenv
Edit the .bashrc obtained from the skel dir to add the differences you have got from the above command.
HTH