On the redemption date, the issuer transfers the principal together with the final coupon, and obligations on the security cease. The bond itself is removed from the depository account, and funds are credited to the investor's brokerage account.
Payments are processed through the accounting infrastructure: the issuer transfers funds, and they reach the final owners through the depository and the nominal holder. Therefore, the credit does not occur instantly on the calendar date, but within the established timeframe.
Early redemption is possible if provided for in the terms of issuance — by offer or by issuer decision. A special case is amortization, in which the principal is returned in parts throughout the entire period, and the final payment constitutes only the remainder.
For an investor holding the security until maturity, intermediate price fluctuations are irrelevant: the result is determined by the yield fixed at purchase, provided the issuer fulfills its obligations. Planning should be done in advance — the returned funds will need to be reinvested at the rates applicable at that time.