It is unlikely that they will completely delete the old method, Apple simply suggests (see "Animations") that you are using the new format.
As indicated, if you want your projects to support iOS and 4.0, continue to use the old format. If not, it is recommended that you upgrade, but if you do not, do not worry about it. (at least until the old format becomes officially obsolete)
EDIT: just re-read the question and answer it specifically; no, neither you nor any other users will experience errors in the future (provided that you use the functions correctly) - even if it becomes obsolete.
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