Contributors to the comp.lang.tcl newsgroup frequently express concern that a decision to use Tcl is risky, because the language might ... well, something might happen.
It's hard to answer unspecified fears rationally. The well-defined ones all turn out to be mistakes. Will Java be better-supported? Well, IBM and Sun have been supporting Java for all its worth, and its portability in particular, and Tcl remains available for a wider span of platforms. Is Tcl vulnerable because its creator might not support it? In fact, John Ousterhout has been away from technical leadership of the implementation since 1999 or so, and new versions continue to appear. Won't GNOME themes, or .NET, or Ruby, or object-orientation, or ..., leave Tcl behind? Sure; in three to five years, each of these will catch up with features Tcl already enjoys. If that means, "leave Tcl behind" to you, then Tcl is probably not a language that will leave you comfortable.
Maybe Tcl will decline in any of several objective senses. The evidence usually presented in support of such a prediction, though, is demonstrably ... inconclusive.
RS Open source software lives as long at least one developer has the sources and can compile them. Tcl sure isn't a fashionable language, but you also often hear how people are surprised and ultimately converted. Yes, we are a minority - but we got The Cool Language!