The wealth of the shareholders is measured by the market value of the shares.
As I explain in my lectures on rights issues, the TERP is the theoretical value of the shares after the rights issue at which shareholders make no gain and no loss.
If it is a question where the money from the rights issue is used to repay bonds (therefore less interest to pay, therefore higher earnings, and therefore higher share price) we calculate the new share price (using a PE valuations). If the new share price is higher than the TERP then shareholder wealth has increased, if it is lower than the TERP then shareholder wealth has fallen.