You can purchase TRS22 (currently a beta version with the full release in March), just like you purchased your copy of TRS19, and you can keep both for ever. TRS19 does not expire. The TRS22 you purchase will have the traditional (Classic) Surveyor 1.0 interface.
You can purchase an annual Trainz Plus subscription, or an annual Gold subscription, and you will receive Trainz Plus (currently in beta with all the features of TRS22) plus a full (non subscription) copy of TRS22 (beta) which you can keep even if you decide not to renew your annual subscription. Both the Trainz Plus and the TRS22 come with the new Surveyor 2.0 (S20) interface. If you do not renew your annual subscription then your copy of TRS22 will revert to the Surveyor 1.0 (Classic) interface and you will lose the S20 features. S20 is a feature of the subscription versions only.